diff --git a/omnistack-kotlin-client-okhttp/src/main/kotlin/com/omnistack/api/client/okhttp/OkHttpClient.kt b/omnistack-kotlin-client-okhttp/src/main/kotlin/com/omnistack/api/client/okhttp/OkHttpClient.kt
index e58b8e2..a4c4eed 100644
--- a/omnistack-kotlin-client-okhttp/src/main/kotlin/com/omnistack/api/client/okhttp/OkHttpClient.kt
+++ b/omnistack-kotlin-client-okhttp/src/main/kotlin/com/omnistack/api/client/okhttp/OkHttpClient.kt
@@ -80,7 +80,7 @@ private constructor(private val okHttpClient: okhttp3.OkHttpClient, private val
 
     private fun HttpRequest.toRequest(): Request {
         var body: RequestBody? = body?.toRequestBody()
-        // OkHttpClient always requires a request body for PUT and POST methods
+        // OkHttpClient always requires a request body for PUT and POST methods.
         if (body == null && (method == HttpMethod.PUT || method == HttpMethod.POST)) {
             body = "".toRequestBody()
         }
@@ -108,21 +108,13 @@ private constructor(private val okHttpClient: okhttp3.OkHttpClient, private val
         val length = contentLength()
 
         return object : RequestBody() {
-            override fun contentType(): MediaType? {
-                return mediaType
-            }
+            override fun contentType(): MediaType? = mediaType
 
-            override fun contentLength(): Long {
-                return length
-            }
+            override fun contentLength(): Long = length
 
-            override fun isOneShot(): Boolean {
-                return !repeatable()
-            }
+            override fun isOneShot(): Boolean = !repeatable()
 
-            override fun writeTo(sink: BufferedSink) {
-                writeTo(sink.outputStream())
-            }
+            override fun writeTo(sink: BufferedSink) = writeTo(sink.outputStream())
         }
     }
 
@@ -130,21 +122,13 @@ private constructor(private val okHttpClient: okhttp3.OkHttpClient, private val
         val headers = headers.toHeaders()
 
         return object : HttpResponse {
-            override fun statusCode(): Int {
-                return code
-            }
+            override fun statusCode(): Int = code
 
-            override fun headers(): ListMultimap<String, String> {
-                return headers
-            }
+            override fun headers(): ListMultimap<String, String> = headers
 
-            override fun body(): InputStream {
-                return body!!.byteStream()
-            }
+            override fun body(): InputStream = body!!.byteStream()
 
-            override fun close() {
-                body!!.close()
-            }
+            override fun close() = body!!.close()
         }
     }
 
@@ -153,9 +137,7 @@ private constructor(private val okHttpClient: okhttp3.OkHttpClient, private val
             MultimapBuilder.treeKeys(String.CASE_INSENSITIVE_ORDER)
                 .arrayListValues()
                 .build<String, String>()
-
         forEach { pair -> headers.put(pair.first, pair.second) }
-
         return headers
     }
 
@@ -166,7 +148,7 @@ private constructor(private val okHttpClient: okhttp3.OkHttpClient, private val
     class Builder {
 
         private var baseUrl: HttpUrl? = null
-        // default timeout is 1 minute
+        // The default timeout is 1 minute.
         private var timeout: Duration = Duration.ofSeconds(60)
         private var proxy: Proxy? = null
 
@@ -176,8 +158,8 @@ private constructor(private val okHttpClient: okhttp3.OkHttpClient, private val
 
         fun proxy(proxy: Proxy?) = apply { this.proxy = proxy }
 
-        fun build(): OkHttpClient {
-            return OkHttpClient(
+        fun build(): OkHttpClient =
+            OkHttpClient(
                 okhttp3.OkHttpClient.Builder()
                     .connectTimeout(timeout)
                     .readTimeout(timeout)
@@ -187,7 +169,6 @@ private constructor(private val okHttpClient: okhttp3.OkHttpClient, private val
                     .build(),
                 checkNotNull(baseUrl) { "`baseUrl` is required but was not set" },
             )
-        }
     }
 
     private suspend fun Call.executeAsync(): Response =
diff --git a/omnistack-kotlin-client-okhttp/src/main/kotlin/com/omnistack/api/client/okhttp/OmnistackOkHttpClient.kt b/omnistack-kotlin-client-okhttp/src/main/kotlin/com/omnistack/api/client/okhttp/OmnistackOkHttpClient.kt
index c686a0e..edbc614 100644
--- a/omnistack-kotlin-client-okhttp/src/main/kotlin/com/omnistack/api/client/okhttp/OmnistackOkHttpClient.kt
+++ b/omnistack-kotlin-client-okhttp/src/main/kotlin/com/omnistack/api/client/okhttp/OmnistackOkHttpClient.kt
@@ -23,7 +23,7 @@ class OmnistackOkHttpClient private constructor() {
 
         private var clientOptions: ClientOptions.Builder = ClientOptions.builder()
         private var baseUrl: String = ClientOptions.PRODUCTION_URL
-        // default timeout for client is 1 minute
+        // The default timeout for the client is 1 minute.
         private var timeout: Duration = Duration.ofSeconds(60)
         private var proxy: Proxy? = null
 
@@ -52,6 +52,24 @@ class OmnistackOkHttpClient private constructor() {
 
         fun removeHeader(name: String) = apply { clientOptions.removeHeader(name) }
 
+        fun queryParams(queryParams: Map<String, Iterable<String>>) = apply {
+            clientOptions.queryParams(queryParams)
+        }
+
+        fun putQueryParam(key: String, value: String) = apply {
+            clientOptions.putQueryParam(key, value)
+        }
+
+        fun putQueryParams(key: String, values: Iterable<String>) = apply {
+            clientOptions.putQueryParams(key, values)
+        }
+
+        fun putAllQueryParams(queryParams: Map<String, Iterable<String>>) = apply {
+            clientOptions.putAllQueryParams(queryParams)
+        }
+
+        fun removeQueryParam(key: String) = apply { clientOptions.removeQueryParam(key) }
+
         fun timeout(timeout: Duration) = apply { this.timeout = timeout }
 
         fun maxRetries(maxRetries: Int) = apply { clientOptions.maxRetries(maxRetries) }
@@ -66,8 +84,8 @@ class OmnistackOkHttpClient private constructor() {
 
         fun fromEnv() = apply { clientOptions.fromEnv() }
 
-        fun build(): OmnistackClient {
-            return OmnistackClientImpl(
+        fun build(): OmnistackClient =
+            OmnistackClientImpl(
                 clientOptions
                     .httpClient(
                         OkHttpClient.builder()
@@ -78,6 +96,5 @@ class OmnistackOkHttpClient private constructor() {
                     )
                     .build()
             )
-        }
     }
 }
diff --git a/omnistack-kotlin-client-okhttp/src/main/kotlin/com/omnistack/api/client/okhttp/OmnistackOkHttpClientAsync.kt b/omnistack-kotlin-client-okhttp/src/main/kotlin/com/omnistack/api/client/okhttp/OmnistackOkHttpClientAsync.kt
index 9f17683..74af000 100644
--- a/omnistack-kotlin-client-okhttp/src/main/kotlin/com/omnistack/api/client/okhttp/OmnistackOkHttpClientAsync.kt
+++ b/omnistack-kotlin-client-okhttp/src/main/kotlin/com/omnistack/api/client/okhttp/OmnistackOkHttpClientAsync.kt
@@ -23,7 +23,7 @@ class OmnistackOkHttpClientAsync private constructor() {
 
         private var clientOptions: ClientOptions.Builder = ClientOptions.builder()
         private var baseUrl: String = ClientOptions.PRODUCTION_URL
-        // default timeout for client is 1 minute
+        // The default timeout for the client is 1 minute.
         private var timeout: Duration = Duration.ofSeconds(60)
         private var proxy: Proxy? = null
 
@@ -52,6 +52,24 @@ class OmnistackOkHttpClientAsync private constructor() {
 
         fun removeHeader(name: String) = apply { clientOptions.removeHeader(name) }
 
+        fun queryParams(queryParams: Map<String, Iterable<String>>) = apply {
+            clientOptions.queryParams(queryParams)
+        }
+
+        fun putQueryParam(key: String, value: String) = apply {
+            clientOptions.putQueryParam(key, value)
+        }
+
+        fun putQueryParams(key: String, values: Iterable<String>) = apply {
+            clientOptions.putQueryParams(key, values)
+        }
+
+        fun putAllQueryParams(queryParams: Map<String, Iterable<String>>) = apply {
+            clientOptions.putAllQueryParams(queryParams)
+        }
+
+        fun removeQueryParam(key: String) = apply { clientOptions.removeQueryParam(key) }
+
         fun timeout(timeout: Duration) = apply { this.timeout = timeout }
 
         fun maxRetries(maxRetries: Int) = apply { clientOptions.maxRetries(maxRetries) }
@@ -66,8 +84,8 @@ class OmnistackOkHttpClientAsync private constructor() {
 
         fun fromEnv() = apply { clientOptions.fromEnv() }
 
-        fun build(): OmnistackClientAsync {
-            return OmnistackClientAsyncImpl(
+        fun build(): OmnistackClientAsync =
+            OmnistackClientAsyncImpl(
                 clientOptions
                     .httpClient(
                         OkHttpClient.builder()
@@ -78,6 +96,5 @@ class OmnistackOkHttpClientAsync private constructor() {
                     )
                     .build()
             )
-        }
     }
 }
diff --git a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/client/OmnistackClient.kt b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/client/OmnistackClient.kt
index 7e0e1e8..8f1caca 100644
--- a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/client/OmnistackClient.kt
+++ b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/client/OmnistackClient.kt
@@ -1,7 +1,5 @@
 // File generated from our OpenAPI spec by Stainless.
 
-@file:Suppress("OVERLOADS_INTERFACE") // See https://youtrack.jetbrains.com/issue/KT-36102
-
 package com.omnistack.api.client
 
 import com.omnistack.api.models.*
diff --git a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/client/OmnistackClientAsync.kt b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/client/OmnistackClientAsync.kt
index 7be4583..40a86dc 100644
--- a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/client/OmnistackClientAsync.kt
+++ b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/client/OmnistackClientAsync.kt
@@ -1,7 +1,5 @@
 // File generated from our OpenAPI spec by Stainless.
 
-@file:Suppress("OVERLOADS_INTERFACE") // See https://youtrack.jetbrains.com/issue/KT-36102
-
 package com.omnistack.api.client
 
 import com.omnistack.api.models.*
diff --git a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/client/OmnistackClientAsyncImpl.kt b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/client/OmnistackClientAsyncImpl.kt
index 769a258..da7ac3f 100644
--- a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/client/OmnistackClientAsyncImpl.kt
+++ b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/client/OmnistackClientAsyncImpl.kt
@@ -3,6 +3,7 @@
 package com.omnistack.api.client
 
 import com.omnistack.api.core.ClientOptions
+import com.omnistack.api.core.getPackageVersion
 import com.omnistack.api.models.*
 import com.omnistack.api.services.async.*
 
@@ -11,12 +12,21 @@ constructor(
     private val clientOptions: ClientOptions,
 ) : OmnistackClientAsync {
 
+    private val clientOptionsWithUserAgent =
+        if (clientOptions.headers.containsKey("User-Agent")) clientOptions
+        else
+            clientOptions
+                .toBuilder()
+                .putHeader("User-Agent", "${javaClass.simpleName}/Kotlin ${getPackageVersion()}")
+                .build()
+
+    // Pass the original clientOptions so that this client sets its own User-Agent.
     private val sync: OmnistackClient by lazy { OmnistackClientImpl(clientOptions) }
 
-    private val chats: ChatServiceAsync by lazy { ChatServiceAsyncImpl(clientOptions) }
+    private val chats: ChatServiceAsync by lazy { ChatServiceAsyncImpl(clientOptionsWithUserAgent) }
 
     private val completions: CompletionServiceAsync by lazy {
-        CompletionServiceAsyncImpl(clientOptions)
+        CompletionServiceAsyncImpl(clientOptionsWithUserAgent)
     }
 
     override fun sync(): OmnistackClient = sync
diff --git a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/client/OmnistackClientImpl.kt b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/client/OmnistackClientImpl.kt
index 32366df..f01afba 100644
--- a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/client/OmnistackClientImpl.kt
+++ b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/client/OmnistackClientImpl.kt
@@ -3,6 +3,7 @@
 package com.omnistack.api.client
 
 import com.omnistack.api.core.ClientOptions
+import com.omnistack.api.core.getPackageVersion
 import com.omnistack.api.models.*
 import com.omnistack.api.services.blocking.*
 
@@ -11,11 +12,22 @@ constructor(
     private val clientOptions: ClientOptions,
 ) : OmnistackClient {
 
+    private val clientOptionsWithUserAgent =
+        if (clientOptions.headers.containsKey("User-Agent")) clientOptions
+        else
+            clientOptions
+                .toBuilder()
+                .putHeader("User-Agent", "${javaClass.simpleName}/Kotlin ${getPackageVersion()}")
+                .build()
+
+    // Pass the original clientOptions so that this client sets its own User-Agent.
     private val async: OmnistackClientAsync by lazy { OmnistackClientAsyncImpl(clientOptions) }
 
-    private val chats: ChatService by lazy { ChatServiceImpl(clientOptions) }
+    private val chats: ChatService by lazy { ChatServiceImpl(clientOptionsWithUserAgent) }
 
-    private val completions: CompletionService by lazy { CompletionServiceImpl(clientOptions) }
+    private val completions: CompletionService by lazy {
+        CompletionServiceImpl(clientOptionsWithUserAgent)
+    }
 
     override fun async(): OmnistackClientAsync = async
 
diff --git a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/core/ClientOptions.kt b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/core/ClientOptions.kt
index 7605cfc..da1abc8 100644
--- a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/core/ClientOptions.kt
+++ b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/core/ClientOptions.kt
@@ -6,21 +6,26 @@ import com.fasterxml.jackson.databind.json.JsonMapper
 import com.google.common.collect.ArrayListMultimap
 import com.google.common.collect.ListMultimap
 import com.omnistack.api.core.http.HttpClient
+import com.omnistack.api.core.http.PhantomReachableClosingHttpClient
 import com.omnistack.api.core.http.RetryingHttpClient
 import java.time.Clock
 
 class ClientOptions
 private constructor(
+    private val originalHttpClient: HttpClient,
     val httpClient: HttpClient,
     val jsonMapper: JsonMapper,
     val clock: Clock,
     val baseUrl: String,
-    val apiKey: String,
     val headers: ListMultimap<String, String>,
     val queryParams: ListMultimap<String, String>,
     val responseValidation: Boolean,
+    val maxRetries: Int,
+    val apiKey: String,
 ) {
 
+    fun toBuilder() = Builder().from(this)
+
     companion object {
 
         const val PRODUCTION_URL = "https://api.omnistack.sh/openai/v1"
@@ -33,60 +38,68 @@ private constructor(
     class Builder {
 
         private var httpClient: HttpClient? = null
-        private var jsonMapper: JsonMapper? = null
+        private var jsonMapper: JsonMapper = jsonMapper()
         private var clock: Clock = Clock.systemUTC()
         private var baseUrl: String = PRODUCTION_URL
-        private var headers: MutableMap<String, MutableList<String>> = mutableMapOf()
-        private var queryParams: MutableMap<String, MutableList<String>> = mutableMapOf()
+        private var headers: ListMultimap<String, String> = ArrayListMultimap.create()
+        private var queryParams: ListMultimap<String, String> = ArrayListMultimap.create()
         private var responseValidation: Boolean = false
         private var maxRetries: Int = 2
         private var apiKey: String? = null
 
+        internal fun from(clientOptions: ClientOptions) = apply {
+            httpClient = clientOptions.originalHttpClient
+            jsonMapper = clientOptions.jsonMapper
+            clock = clientOptions.clock
+            baseUrl = clientOptions.baseUrl
+            headers = ArrayListMultimap.create(clientOptions.headers)
+            queryParams = ArrayListMultimap.create(clientOptions.queryParams)
+            responseValidation = clientOptions.responseValidation
+            maxRetries = clientOptions.maxRetries
+            apiKey = clientOptions.apiKey
+        }
+
         fun httpClient(httpClient: HttpClient) = apply { this.httpClient = httpClient }
 
         fun jsonMapper(jsonMapper: JsonMapper) = apply { this.jsonMapper = jsonMapper }
 
-        fun baseUrl(baseUrl: String) = apply { this.baseUrl = baseUrl }
-
         fun clock(clock: Clock) = apply { this.clock = clock }
 
+        fun baseUrl(baseUrl: String) = apply { this.baseUrl = baseUrl }
+
         fun headers(headers: Map<String, Iterable<String>>) = apply {
             this.headers.clear()
             putAllHeaders(headers)
         }
 
-        fun putHeader(name: String, value: String) = apply {
-            this.headers.getOrPut(name) { mutableListOf() }.add(value)
-        }
+        fun putHeader(name: String, value: String) = apply { headers.put(name, value) }
 
         fun putHeaders(name: String, values: Iterable<String>) = apply {
-            this.headers.getOrPut(name) { mutableListOf() }.addAll(values)
+            headers.putAll(name, values)
         }
 
         fun putAllHeaders(headers: Map<String, Iterable<String>>) = apply {
-            headers.forEach(this::putHeaders)
+            headers.forEach(::putHeaders)
         }
 
-        fun removeHeader(name: String) = apply { this.headers.put(name, mutableListOf()) }
+        fun removeHeader(name: String) = apply { headers.removeAll(name) }
 
         fun queryParams(queryParams: Map<String, Iterable<String>>) = apply {
             this.queryParams.clear()
             putAllQueryParams(queryParams)
         }
 
-        fun putQueryParam(name: String, value: String) = apply {
-            this.queryParams.getOrPut(name) { mutableListOf() }.add(value)
-        }
+        fun putQueryParam(key: String, value: String) = apply { queryParams.put(key, value) }
 
-        fun putQueryParams(name: String, values: Iterable<String>) = apply {
-            this.queryParams.getOrPut(name) { mutableListOf() }.addAll(values)
+        fun putQueryParams(key: String, values: Iterable<String>) = apply {
+            queryParams.putAll(key, values)
         }
 
         fun putAllQueryParams(queryParams: Map<String, Iterable<String>>) = apply {
-            queryParams.forEach(this::putQueryParams)
+            queryParams.forEach(::putQueryParams)
         }
 
-        fun removeQueryParam(name: String) = apply { this.queryParams.put(name, mutableListOf()) }
+        fun removeQueryParam(key: String) = apply { queryParams.removeAll(key) }
 
         fun responseValidation(responseValidation: Boolean) = apply {
             this.responseValidation = responseValidation
@@ -109,26 +122,31 @@ private constructor(
             headers.put("X-Stainless-OS", getOsName())
             headers.put("X-Stainless-OS-Version", getOsVersion())
             headers.put("X-Stainless-Package-Version", getPackageVersion())
+            headers.put("X-Stainless-Runtime", "JRE")
             headers.put("X-Stainless-Runtime-Version", getJavaVersion())
             if (!apiKey.isNullOrEmpty()) {
                 headers.put("Authorization", "Bearer ${apiKey}")
             }
-            this.headers.forEach(headers::replaceValues)
-            this.queryParams.forEach(queryParams::replaceValues)
+            this.headers.asMap().forEach(headers::replaceValues)
+            this.queryParams.asMap().forEach(queryParams::replaceValues)
 
             return ClientOptions(
-                RetryingHttpClient.builder()
-                    .httpClient(httpClient!!)
-                    .clock(clock)
-                    .maxRetries(maxRetries)
-                    .build(),
-                jsonMapper ?: jsonMapper(),
+                httpClient!!,
+                PhantomReachableClosingHttpClient(
+                    RetryingHttpClient.builder()
+                        .httpClient(httpClient!!)
+                        .clock(clock)
+                        .maxRetries(maxRetries)
+                        .build()
+                ),
+                jsonMapper,
                 clock,
                 baseUrl,
-                apiKey!!,
-                headers.toUnmodifiable(),
-                queryParams.toUnmodifiable(),
+                headers.toImmutable(),
+                queryParams.toImmutable(),
                 responseValidation,
+                maxRetries,
+                apiKey!!,
             )
         }
     }
diff --git a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/core/PhantomReachable.kt b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/core/PhantomReachable.kt
new file mode 100644
index 0000000..db2978d
--- /dev/null
+++ b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/core/PhantomReachable.kt
@@ -0,0 +1,45 @@
+@file:JvmName("PhantomReachable")
+
+package com.omnistack.api.core
+
+import com.omnistack.api.errors.OmnistackException
+import java.lang.reflect.InvocationTargetException
+
+/**
+ * Closes [closeable] when [observed] becomes only phantom reachable.
+ *
+ * This is a wrapper around a Java 9+ [java.lang.ref.Cleaner], or a no-op in older Java versions.
+ */
+internal fun closeWhenPhantomReachable(observed: Any, closeable: AutoCloseable) {
+    check(observed !== closeable) {
+        "`observed` cannot be the same object as `closeable` because it would never become phantom reachable"
+    }
+    closeWhenPhantomReachable?.let { it(observed, closeable::close) }
+}
+
+private val closeWhenPhantomReachable: ((Any, AutoCloseable) -> Unit)? by lazy {
+    try {
+        val cleanerClass = Class.forName("java.lang.ref.Cleaner")
+        val cleanerCreate = cleanerClass.getMethod("create")
+        val cleanerRegister =
+            cleanerClass.getMethod("register", Any::class.java, Runnable::class.java)
+        val cleanerObject = cleanerCreate.invoke(null);
+
+        { observed, closeable ->
+            try {
+                cleanerRegister.invoke(cleanerObject, observed, Runnable { closeable.close() })
+            } catch (e: ReflectiveOperationException) {
+                if (e is InvocationTargetException) {
+                    when (val cause = e.cause) {
+                        is RuntimeException,
+                        is Error -> throw cause
+                    }
+                }
+                throw OmnistackException("Unexpected reflective invocation failure", e)
+            }
+        }
+    } catch (e: ReflectiveOperationException) {
+        // We're running Java 8, which has no Cleaner.
+        null
+    }
+}
diff --git a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/core/Utils.kt b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/core/Utils.kt
index b236402..312ec0b 100644
--- a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/core/Utils.kt
+++ b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/core/Utils.kt
@@ -4,53 +4,24 @@ package com.omnistack.api.core
 
 import com.google.common.collect.ImmutableListMultimap
 import com.google.common.collect.ListMultimap
-import com.google.common.collect.Multimaps
 import com.omnistack.api.errors.OmnistackInvalidDataException
 import java.util.Collections
+import java.util.SortedMap
 
-internal fun <T : Any> T?.getOrThrow(name: String): T {
-    if (this == null) {
-        throw OmnistackInvalidDataException("'${name}' is not present")
-    }
-
-    return this
-}
-
-internal fun <T> List<T>.toUnmodifiable(): List<T> {
-    if (isEmpty()) {
-        return Collections.emptyList()
-    }
-
-    return Collections.unmodifiableList(this)
-}
-
-internal fun <K, V> Map<K, V>.toUnmodifiable(): Map<K, V> {
-    if (isEmpty()) {
-        return Collections.emptyMap()
-    }
-
-    return Collections.unmodifiableMap(this)
-}
-
-internal fun <K, V> ListMultimap<K, V>.toUnmodifiable(): ListMultimap<K, V> {
-    if (isEmpty()) {
-        return ImmutableListMultimap.of()
-    }
-
-    return Multimaps.unmodifiableListMultimap(this)
-}
-
-internal fun ListMultimap<String, String>.getRequiredHeader(header: String): String {
-    val value =
-        entries()
-            .stream()
-            .filter { entry -> entry.key.equals(header, ignoreCase = true) }
-            .map { entry -> entry.value }
-            .findFirst()
-    if (!value.isPresent) {
-        throw OmnistackInvalidDataException("Could not find $header header")
-    }
-    return value.get()
-}
+internal fun <T : Any> T?.getOrThrow(name: String): T =
+    this ?: throw OmnistackInvalidDataException("`${name}` is not present")
+
+internal fun <T> List<T>.toImmutable(): List<T> =
+    if (isEmpty()) Collections.emptyList() else Collections.unmodifiableList(toList())
+
+internal fun <K, V> Map<K, V>.toImmutable(): Map<K, V> =
+    if (isEmpty()) Collections.emptyMap() else Collections.unmodifiableMap(toMap())
+
+internal fun <K : Comparable<K>, V> SortedMap<K, V>.toImmutable(): SortedMap<K, V> =
+    if (isEmpty()) Collections.emptySortedMap()
+    else Collections.unmodifiableSortedMap(toSortedMap(comparator()))
+
+internal fun <K, V> ListMultimap<K, V>.toImmutable(): ListMultimap<K, V> =
+    ImmutableListMultimap.copyOf(this)
 
 internal interface Enum
diff --git a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/core/Values.kt b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/core/Values.kt
index 32ef01a..ad76968 100644
--- a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/core/Values.kt
+++ b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/core/Values.kt
@@ -138,6 +138,8 @@ sealed class JsonField<out T : Any> {
     // This filter should not be used directly and should instead use the @ExcludeMissing annotation
     class IsMissing {
         override fun equals(other: Any?): Boolean = other is JsonMissing
+
+        override fun hashCode(): Int = Objects.hash()
     }
 
     class Deserializer(private val type: JavaType? = null) :
@@ -383,7 +385,7 @@ private constructor(
     override fun toString() = values.toString()
 
     companion object {
-        @JsonCreator fun of(values: List<JsonValue>) = JsonArray(values.toUnmodifiable())
+        @JsonCreator fun of(values: List<JsonValue>) = JsonArray(values.toImmutable())
     }
 }
 
@@ -407,7 +409,7 @@ private constructor(
     override fun toString() = values.toString()
 
     companion object {
-        @JsonCreator fun of(values: Map<String, JsonValue>) = JsonObject(values.toUnmodifiable())
+        @JsonCreator fun of(values: Map<String, JsonValue>) = JsonObject(values.toImmutable())
     }
 }
 
@@ -473,9 +475,8 @@ internal constructor(
         }
     }
 
-    override fun toString(): String {
-        return "MultipartFormValue(name='$name', contentType=$contentType, filename=$filename, value=${valueToString()})"
-    }
+    override fun toString(): String =
+        "MultipartFormValue{name=$name, contentType=$contentType, filename=$filename, value=${valueToString()}}"
 
     private fun valueToString(): String =
         when (value) {
diff --git a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/core/http/Headers.kt b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/core/http/Headers.kt
new file mode 100644
index 0000000..79b172e
--- /dev/null
+++ b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/core/http/Headers.kt
@@ -0,0 +1,88 @@
+package com.omnistack.api.core.http
+
+import com.omnistack.api.core.toImmutable
+import java.util.TreeMap
+
+class Headers private constructor(private val map: Map<String, List<String>>, val size: Int) {
+
+    fun isEmpty(): Boolean = map.isEmpty()
+
+    fun names(): Set<String> = map.keys
+
+    fun values(name: String): List<String> = map[name].orEmpty()
+
+    fun toBuilder(): Builder = Builder().putAll(map)
+
+    companion object {
+
+        fun builder() = Builder()
+    }
+
+    class Builder {
+
+        private val map: MutableMap<String, MutableList<String>> =
+            TreeMap(String.CASE_INSENSITIVE_ORDER)
+        private var size: Int = 0
+
+        fun put(name: String, value: String) = apply {
+            map.getOrPut(name) { mutableListOf() }.add(value)
+            size++
+        }
+
+        fun put(name: String, values: Iterable<String>) = apply { values.forEach { put(name, it) } }
+
+        fun putAll(headers: Map<String, Iterable<String>>) = apply { headers.forEach(::put) }
+
+        fun putAll(headers: Headers) = apply {
+            headers.names().forEach { put(it, headers.values(it)) }
+        }
+
+        fun replace(name: String, value: String) = apply {
+            remove(name)
+            put(name, value)
+        }
+
+        fun replace(name: String, values: Iterable<String>) = apply {
+            remove(name)
+            put(name, values)
+        }
+
+        fun replaceAll(headers: Map<String, Iterable<String>>) = apply {
+            headers.forEach(::replace)
+        }
+
+        fun replaceAll(headers: Headers) = apply {
+            headers.names().forEach { replace(it, headers.values(it)) }
+        }
+
+        fun remove(name: String) = apply { size -= map.remove(name).orEmpty().size }
+
+        fun removeAll(names: Set<String>) = apply { names.forEach(::remove) }
+
+        fun clear() = apply {
+            map.clear()
+            size = 0
+        }
+
+        fun build() =
+            Headers(
+                map.mapValuesTo(TreeMap(String.CASE_INSENSITIVE_ORDER)) { (_, values) ->
+                        values.toImmutable()
+                    }
+                    .toImmutable(),
+                size
+            )
+    }
+
+    override fun hashCode(): Int = map.hashCode()
+
+    override fun equals(other: Any?): Boolean {
+        if (this === other) {
+            return true
+        }
+
+        return other is Headers && map == other.map
+    }
+
+    override fun toString(): String = "Headers{map=$map}"
+}
diff --git a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/core/http/HttpRequest.kt b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/core/http/HttpRequest.kt
index 694ae1b..94a2a2c 100644
--- a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/core/http/HttpRequest.kt
+++ b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/core/http/HttpRequest.kt
@@ -4,7 +4,7 @@ import com.google.common.collect.ArrayListMultimap
 import com.google.common.collect.ListMultimap
 import com.google.common.collect.Multimap
 import com.google.common.collect.MultimapBuilder
-import com.omnistack.api.core.toUnmodifiable
+import com.omnistack.api.core.toImmutable
 
 class HttpRequest
 private constructor(
@@ -17,7 +17,7 @@ private constructor(
 ) {
 
     override fun toString(): String =
-        "HttpRequest {method=$method, pathSegments=$pathSegments, queryParams=$queryParams, headers=$headers, body=$body}"
+        "HttpRequest{method=$method, pathSegments=$pathSegments, queryParams=$queryParams, headers=$headers, body=$body}"
 
     companion object {
         fun builder() = Builder()
@@ -83,8 +83,8 @@ private constructor(
             HttpRequest(
                 checkNotNull(method) { "`method` is required but was not set" },
                 url,
-                pathSegments.toUnmodifiable(),
-                queryParams.toUnmodifiable(),
+                pathSegments.toImmutable(),
+                queryParams.toImmutable(),
                 headers,
                 body,
             )
diff --git a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/core/http/PhantomReachableClosingHttpClient.kt b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/core/http/PhantomReachableClosingHttpClient.kt
new file mode 100644
index 0000000..e525da5
--- /dev/null
+++ b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/core/http/PhantomReachableClosingHttpClient.kt
@@ -0,0 +1,20 @@
+package com.omnistack.api.core.http
+
+import com.omnistack.api.core.RequestOptions
+import com.omnistack.api.core.closeWhenPhantomReachable
+
+internal class PhantomReachableClosingHttpClient(private val httpClient: HttpClient) : HttpClient {
+    init {
+        closeWhenPhantomReachable(this, httpClient)
+    }
+
+    override fun execute(request: HttpRequest, requestOptions: RequestOptions): HttpResponse =
+        httpClient.execute(request, requestOptions)
+
+    override suspend fun executeAsync(
+        request: HttpRequest,
+        requestOptions: RequestOptions
+    ): HttpResponse = httpClient.executeAsync(request, requestOptions)
+
+    override fun close() = httpClient.close()
+}
diff --git a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/core/http/QueryParams.kt b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/core/http/QueryParams.kt
new file mode 100644
index 0000000..9ed8488
--- /dev/null
+++ b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/core/http/QueryParams.kt
@@ -0,0 +1,82 @@
+package com.omnistack.api.core.http
+
+import com.omnistack.api.core.toImmutable
+
+class QueryParams private constructor(private val map: Map<String, List<String>>, val size: Int) {
+
+    fun isEmpty(): Boolean = map.isEmpty()
+
+    fun keys(): Set<String> = map.keys
+
+    fun values(key: String): List<String> = map[key].orEmpty()
+
+    fun toBuilder(): Builder = Builder().putAll(map)
+
+    companion object {
+
+        fun builder() = Builder()
+    }
+
+    class Builder {
+
+        private val map: MutableMap<String, MutableList<String>> = mutableMapOf()
+        private var size: Int = 0
+
+        fun put(key: String, value: String) = apply {
+            map.getOrPut(key) { mutableListOf() }.add(value)
+            size++
+        }
+
+        fun put(key: String, values: Iterable<String>) = apply { values.forEach { put(key, it) } }
+
+        fun putAll(queryParams: Map<String, Iterable<String>>) = apply {
+            queryParams.forEach(::put)
+        }
+
+        fun putAll(queryParams: QueryParams) = apply {
+            queryParams.keys().forEach { put(it, queryParams.values(it)) }
+        }
+
+        fun replace(key: String, value: String) = apply {
+            remove(key)
+            put(key, value)
+        }
+
+        fun replace(key: String, values: Iterable<String>) = apply {
+            remove(key)
+            put(key, values)
+        }
+
+        fun replaceAll(queryParams: Map<String, Iterable<String>>) = apply {
+            queryParams.forEach(::replace)
+        }
+
+        fun replaceAll(queryParams: QueryParams) = apply {
+            queryParams.keys().forEach { replace(it, queryParams.values(it)) }
+        }
+
+        fun remove(key: String) = apply { size -= map.remove(key).orEmpty().size }
+
+        fun removeAll(keys: Set<String>) = apply { keys.forEach(::remove) }
+
+        fun clear() = apply {
+            map.clear()
+            size = 0
+        }
+
+        fun build() =
+            QueryParams(map.mapValues { (_, values) -> values.toImmutable() }.toImmutable(), size)
+    }
+
+    override fun hashCode(): Int = map.hashCode()
+
+    override fun equals(other: Any?): Boolean {
+        if (this === other) {
+            return true
+        }
+
+        return other is QueryParams && map == other.map
+    }
+
+    override fun toString(): String = "QueryParams{map=$map}"
+}
diff --git a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/core/http/RetryingHttpClient.kt b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/core/http/RetryingHttpClient.kt
index 3ae47f9..95b6809 100644
--- a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/core/http/RetryingHttpClient.kt
+++ b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/core/http/RetryingHttpClient.kt
@@ -1,5 +1,3 @@
-@file:JvmSynthetic
-
 package com.omnistack.api.core.http
 
 import com.omnistack.api.core.RequestOptions
@@ -109,15 +107,12 @@ private constructor(
         }
     }
 
-    override fun close() {
-        httpClient.close()
-    }
+    override fun close() = httpClient.close()
 
-    private fun isRetryable(request: HttpRequest): Boolean {
+    private fun isRetryable(request: HttpRequest): Boolean =
         // Some requests, such as when a request body is being streamed, cannot be retried because
         // the body data aren't available on subsequent attempts.
-        return request.body?.repeatable() ?: true
-    }
+        request.body?.repeatable() ?: true
 
     private fun setRetryCountHeader(request: HttpRequest, retries: Int) {
         request.headers.removeAll("x-stainless-retry-count")
@@ -155,11 +150,10 @@ private constructor(
         }
     }
 
-    private fun shouldRetry(throwable: Throwable): Boolean {
+    private fun shouldRetry(throwable: Throwable): Boolean =
         // Only retry IOException and OmnistackIoException, other exceptions are not intended to be
         // retried.
-        return throwable is IOException || throwable is OmnistackIoException
-    }
+        throwable is IOException || throwable is OmnistackIoException
 
     private fun getRetryBackoffMillis(retries: Int, response: HttpResponse?): Duration {
         // About the Retry-After header:
diff --git a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/errors/OmnistackError.kt b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/errors/OmnistackError.kt
index 0835fba..b468a6c 100644
--- a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/errors/OmnistackError.kt
+++ b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/errors/OmnistackError.kt
@@ -7,7 +7,7 @@ import com.fasterxml.jackson.annotation.JsonAnySetter
 import com.fasterxml.jackson.databind.annotation.JsonDeserialize
 import com.omnistack.api.core.JsonValue
 import com.omnistack.api.core.NoAutoDetect
-import com.omnistack.api.core.toUnmodifiable
+import com.omnistack.api.core.toImmutable
 import java.util.Objects
 
 @JsonDeserialize(builder = OmnistackError.Builder::class)
@@ -37,7 +37,7 @@ constructor(
 
     companion object {
 
-        @JvmStatic fun builder() = Builder()
+        fun builder() = Builder()
     }
 
     class Builder {
@@ -60,6 +60,6 @@ constructor(
             this.additionalProperties.putAll(additionalProperties)
         }
 
-        fun build(): OmnistackError = OmnistackError(additionalProperties.toUnmodifiable())
+        fun build(): OmnistackError = OmnistackError(additionalProperties.toImmutable())
     }
 }
diff --git a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/models/ChatCompletionCreateParams.kt b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/models/ChatCompletionCreateParams.kt
index e76e34f..46c9a20 100644
--- a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/models/ChatCompletionCreateParams.kt
+++ b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/models/ChatCompletionCreateParams.kt
@@ -22,7 +22,7 @@ import com.omnistack.api.core.JsonMissing
 import com.omnistack.api.core.JsonValue
 import com.omnistack.api.core.NoAutoDetect
 import com.omnistack.api.core.getOrThrow
-import com.omnistack.api.core.toUnmodifiable
+import com.omnistack.api.core.toImmutable
 import com.omnistack.api.errors.OmnistackInvalidDataException
 import com.omnistack.api.models.*
 import java.util.Objects
@@ -709,11 +709,11 @@ constructor(
             fun build(): ChatCompletionCreateBody =
                 ChatCompletionCreateBody(
                     checkNotNull(messages) { "`messages` is required but was not set" }
-                        .toUnmodifiable(),
+                        .toImmutable(),
                     checkNotNull(model) { "`model` is required but was not set" },
                     frequencyPenalty,
                     functionCall,
-                    functions?.toUnmodifiable(),
+                    functions?.toImmutable(),
                     logitBias,
                     logprobs,
                     maxCompletionTokens,
@@ -729,11 +729,11 @@ constructor(
                     streamOptions,
                     temperature,
                     toolChoice,
-                    tools?.toUnmodifiable(),
+                    tools?.toImmutable(),
                     topLogprobs,
                     topP,
                     user,
-                    additionalProperties.toUnmodifiable(),
+                    additionalProperties.toImmutable(),
                 )
         }
 
@@ -1315,12 +1315,11 @@ constructor(
 
         fun build(): ChatCompletionCreateParams =
             ChatCompletionCreateParams(
-                checkNotNull(messages) { "`messages` is required but was not set" }
-                    .toUnmodifiable(),
+                checkNotNull(messages) { "`messages` is required but was not set" }.toImmutable(),
                 checkNotNull(model) { "`model` is required but was not set" },
                 frequencyPenalty,
                 functionCall,
-                if (functions.size == 0) null else functions.toUnmodifiable(),
+                if (functions.size == 0) null else functions.toImmutable(),
                 logitBias,
                 logprobs,
                 maxCompletionTokens,
@@ -1336,13 +1335,13 @@ constructor(
                 streamOptions,
                 temperature,
                 toolChoice,
-                if (tools.size == 0) null else tools.toUnmodifiable(),
+                if (tools.size == 0) null else tools.toImmutable(),
                 topLogprobs,
                 topP,
                 user,
-                additionalQueryParams.mapValues { it.value.toUnmodifiable() }.toUnmodifiable(),
-                additionalHeaders.mapValues { it.value.toUnmodifiable() }.toUnmodifiable(),
-                additionalBodyProperties.toUnmodifiable(),
+                additionalQueryParams.mapValues { it.value.toImmutable() }.toImmutable(),
+                additionalHeaders.mapValues { it.value.toImmutable() }.toImmutable(),
+                additionalBodyProperties.toImmutable(),
             )
     }
 
@@ -1537,6 +1536,7 @@ constructor(
 
             override fun ObjectCodec.deserialize(node: JsonNode): Message {
                 val json = JsonValue.fromJsonNode(node)
+
                 tryDeserialize(node, jacksonTypeRef<ChatCompletionRequestSystemMessage>()) {
                         it.validate()
                     }
@@ -1718,7 +1718,7 @@ constructor(
                         content,
                         role,
                         name,
-                        additionalProperties.toUnmodifiable(),
+                        additionalProperties.toImmutable(),
                     )
             }
 
@@ -1822,6 +1822,7 @@ constructor(
 
                     override fun ObjectCodec.deserialize(node: JsonNode): Content {
                         val json = JsonValue.fromJsonNode(node)
+
                         tryDeserialize(node, jacksonTypeRef<String>())?.let {
                             return Content(textContent = it, _json = json)
                         }
@@ -1953,7 +1954,7 @@ constructor(
                             ChatCompletionRequestMessageContentPartText(
                                 type,
                                 text,
-                                additionalProperties.toUnmodifiable(),
+                                additionalProperties.toImmutable(),
                             )
                     }
 
@@ -2225,7 +2226,7 @@ constructor(
                         content,
                         role,
                         name,
-                        additionalProperties.toUnmodifiable(),
+                        additionalProperties.toImmutable(),
                     )
             }
 
@@ -2330,6 +2331,7 @@ constructor(
 
                     override fun ObjectCodec.deserialize(node: JsonNode): Content {
                         val json = JsonValue.fromJsonNode(node)
+
                         tryDeserialize(node, jacksonTypeRef<String>())?.let {
                             return Content(textContent = it, _json = json)
                         }
@@ -2515,6 +2517,7 @@ constructor(
                             node: JsonNode
                         ): ChatCompletionRequestUserMessageContentPart {
                             val json = JsonValue.fromJsonNode(node)
+
                             tryDeserialize(
                                     node,
                                     jacksonTypeRef<ChatCompletionRequestMessageContentPartText>()
@@ -2669,7 +2672,7 @@ constructor(
                                 ChatCompletionRequestMessageContentPartText(
                                     type,
                                     text,
-                                    additionalProperties.toUnmodifiable(),
+                                    additionalProperties.toImmutable(),
                                 )
                         }
 
@@ -2844,7 +2847,7 @@ constructor(
                                 ChatCompletionRequestMessageContentPartImage(
                                     type,
                                     imageUrl,
-                                    additionalProperties.toUnmodifiable(),
+                                    additionalProperties.toImmutable(),
                                 )
                         }
 
@@ -2954,7 +2957,7 @@ constructor(
                                     ImageUrl(
                                         url,
                                         detail,
-                                        additionalProperties.toUnmodifiable(),
+                                        additionalProperties.toImmutable(),
                                     )
                             }
 
@@ -3400,9 +3403,9 @@ constructor(
                         refusal,
                         role,
                         name,
-                        toolCalls.map { it.toUnmodifiable() },
+                        toolCalls.map { it.toImmutable() },
                         functionCall,
-                        additionalProperties.toUnmodifiable(),
+                        additionalProperties.toImmutable(),
                     )
             }
 
@@ -3557,6 +3560,7 @@ constructor(
 
                     override fun ObjectCodec.deserialize(node: JsonNode): Content {
                         val json = JsonValue.fromJsonNode(node)
+
                         tryDeserialize(node, jacksonTypeRef<String>())?.let {
                             return Content(textContent = it, _json = json)
                         }
@@ -3744,6 +3748,7 @@ constructor(
                             node: JsonNode
                         ): ChatCompletionRequestAssistantMessageContentPart {
                             val json = JsonValue.fromJsonNode(node)
+
                             tryDeserialize(
                                     node,
                                     jacksonTypeRef<ChatCompletionRequestMessageContentPartText>()
@@ -3898,7 +3903,7 @@ constructor(
                                 ChatCompletionRequestMessageContentPartText(
                                     type,
                                     text,
-                                    additionalProperties.toUnmodifiable(),
+                                    additionalProperties.toImmutable(),
                                 )
                         }
 
@@ -4077,7 +4082,7 @@ constructor(
                                 ChatCompletionRequestMessageContentPartRefusal(
                                     type,
                                     refusal,
-                                    additionalProperties.toUnmodifiable(),
+                                    additionalProperties.toImmutable(),
                                 )
                         }
 
@@ -4272,7 +4277,7 @@ constructor(
                         FunctionCall(
                             arguments,
                             name,
-                            additionalProperties.toUnmodifiable(),
+                            additionalProperties.toImmutable(),
                         )
                 }
 
@@ -4405,7 +4410,7 @@ constructor(
                             id,
                             type,
                             function,
-                            additionalProperties.toUnmodifiable(),
+                            additionalProperties.toImmutable(),
                         )
                 }
 
@@ -4522,7 +4527,7 @@ constructor(
                             Function(
                                 name,
                                 arguments,
-                                additionalProperties.toUnmodifiable(),
+                                additionalProperties.toImmutable(),
                             )
                     }
 
@@ -4753,7 +4758,7 @@ constructor(
                         role,
                         content,
                         toolCallId,
-                        additionalProperties.toUnmodifiable(),
+                        additionalProperties.toImmutable(),
                     )
             }
 
@@ -4857,6 +4862,7 @@ constructor(
 
                     override fun ObjectCodec.deserialize(node: JsonNode): Content {
                         val json = JsonValue.fromJsonNode(node)
+
                         tryDeserialize(node, jacksonTypeRef<String>())?.let {
                             return Content(textContent = it, _json = json)
                         }
@@ -4988,7 +4994,7 @@ constructor(
                             ChatCompletionRequestMessageContentPartText(
                                 type,
                                 text,
-                                additionalProperties.toUnmodifiable(),
+                                additionalProperties.toImmutable(),
                             )
                     }
 
@@ -5248,7 +5254,7 @@ constructor(
                         role,
                         content,
                         name,
-                        additionalProperties.toUnmodifiable(),
+                        additionalProperties.toImmutable(),
                     )
             }
 
@@ -5410,6 +5416,7 @@ constructor(
 
             override fun ObjectCodec.deserialize(node: JsonNode): Model {
                 val json = JsonValue.fromJsonNode(node)
+
                 tryDeserialize(node, jacksonTypeRef<String>())?.let {
                     return Model(string = it, _json = json)
                 }
@@ -5759,6 +5766,7 @@ constructor(
 
             override fun ObjectCodec.deserialize(node: JsonNode): FunctionCall {
                 val json = JsonValue.fromJsonNode(node)
+
                 tryDeserialize(node, jacksonTypeRef<UnionMember0>())?.let {
                     return FunctionCall(unionMember0 = it, _json = json)
                 }
@@ -5921,7 +5929,7 @@ constructor(
                     }
 
                 fun build(): ChatCompletionFunctionCallOption =
-                    ChatCompletionFunctionCallOption(name, additionalProperties.toUnmodifiable())
+                    ChatCompletionFunctionCallOption(name, additionalProperties.toImmutable())
             }
 
             override fun equals(other: Any?): Boolean {
@@ -6046,7 +6054,7 @@ constructor(
                     description,
                     checkNotNull(name) { "`name` is required but was not set" },
                     parameters,
-                    additionalProperties.toUnmodifiable(),
+                    additionalProperties.toImmutable(),
                 )
         }
 
@@ -6099,7 +6107,7 @@ constructor(
                         this.additionalProperties.putAll(additionalProperties)
                     }
 
-                fun build(): Parameters = Parameters(additionalProperties.toUnmodifiable())
+                fun build(): Parameters = Parameters(additionalProperties.toImmutable())
             }
 
             override fun equals(other: Any?): Boolean {
@@ -6192,7 +6200,7 @@ constructor(
                 this.additionalProperties.putAll(additionalProperties)
             }
 
-            fun build(): LogitBias = LogitBias(additionalProperties.toUnmodifiable())
+            fun build(): LogitBias = LogitBias(additionalProperties.toImmutable())
         }
 
         override fun equals(other: Any?): Boolean {
@@ -6331,6 +6339,7 @@ constructor(
 
             override fun ObjectCodec.deserialize(node: JsonNode): ResponseFormat {
                 val json = JsonValue.fromJsonNode(node)
+
                 tryDeserialize(node, jacksonTypeRef<ResponseFormatText>()) { it.validate() }
                     ?.let {
                         return ResponseFormat(responseFormatText = it, _json = json)
@@ -6436,7 +6445,7 @@ constructor(
                     }
 
                 fun build(): ResponseFormatText =
-                    ResponseFormatText(type, additionalProperties.toUnmodifiable())
+                    ResponseFormatText(type, additionalProperties.toImmutable())
             }
 
             class Type
@@ -6579,7 +6588,7 @@ constructor(
                     }
 
                 fun build(): ResponseFormatJsonObject =
-                    ResponseFormatJsonObject(type, additionalProperties.toUnmodifiable())
+                    ResponseFormatJsonObject(type, additionalProperties.toImmutable())
             }
 
             class Type
@@ -6741,7 +6750,7 @@ constructor(
                     ResponseFormatJsonSchema(
                         type,
                         jsonSchema,
-                        additionalProperties.toUnmodifiable(),
+                        additionalProperties.toImmutable(),
                     )
             }
 
@@ -6920,7 +6929,7 @@ constructor(
                             name,
                             schema,
                             strict,
-                            additionalProperties.toUnmodifiable(),
+                            additionalProperties.toImmutable(),
                         )
                 }
 
@@ -6975,7 +6984,7 @@ constructor(
                             additionalProperties: Map<String, JsonValue>
                         ) = apply { this.additionalProperties.putAll(additionalProperties) }
 
-                        fun build(): Schema = Schema(additionalProperties.toUnmodifiable())
+                        fun build(): Schema = Schema(additionalProperties.toImmutable())
                     }
 
                     override fun equals(other: Any?): Boolean {
@@ -7234,6 +7243,7 @@ constructor(
 
             override fun ObjectCodec.deserialize(node: JsonNode): Stop {
                 val json = JsonValue.fromJsonNode(node)
+
                 tryDeserialize(node, jacksonTypeRef<String>())?.let {
                     return Stop(string = it, _json = json)
                 }
@@ -7324,7 +7334,7 @@ constructor(
             }
 
             fun build(): StreamOptions =
-                StreamOptions(includeUsage, additionalProperties.toUnmodifiable())
+                StreamOptions(includeUsage, additionalProperties.toImmutable())
         }
 
         override fun equals(other: Any?): Boolean {
@@ -7450,6 +7460,7 @@ constructor(
 
             override fun ObjectCodec.deserialize(node: JsonNode): ToolChoice {
                 val json = JsonValue.fromJsonNode(node)
+
                 tryDeserialize(node, jacksonTypeRef<UnionMember0>())?.let {
                     return ToolChoice(unionMember0 = it, _json = json)
                 }
@@ -7634,7 +7645,7 @@ constructor(
                     ChatCompletionNamedToolChoice(
                         type,
                         function,
-                        additionalProperties.toUnmodifiable(),
+                        additionalProperties.toImmutable(),
                     )
             }
 
@@ -7705,7 +7716,7 @@ constructor(
                             this.additionalProperties.putAll(additionalProperties)
                         }
 
-                    fun build(): Function = Function(name, additionalProperties.toUnmodifiable())
+                    fun build(): Function = Function(name, additionalProperties.toImmutable())
                 }
 
                 override fun equals(other: Any?): Boolean {
@@ -7863,7 +7874,7 @@ constructor(
                 Tool(
                     checkNotNull(type) { "`type` is required but was not set" },
                     checkNotNull(function) { "`function` is required but was not set" },
-                    additionalProperties.toUnmodifiable(),
+                    additionalProperties.toImmutable(),
                 )
         }
 
@@ -7989,7 +8000,7 @@ constructor(
                         checkNotNull(name) { "`name` is required but was not set" },
                         parameters,
                         strict,
-                        additionalProperties.toUnmodifiable(),
+                        additionalProperties.toImmutable(),
                     )
             }
 
@@ -8042,7 +8053,7 @@ constructor(
                             this.additionalProperties.putAll(additionalProperties)
                         }
 
-                    fun build(): Parameters = Parameters(additionalProperties.toUnmodifiable())
+                    fun build(): Parameters = Parameters(additionalProperties.toImmutable())
                 }
 
                 override fun equals(other: Any?): Boolean {
diff --git a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/models/ChatCompletionCreateResponse.kt b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/models/ChatCompletionCreateResponse.kt
index 869e9e4..d9acc67 100644
--- a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/models/ChatCompletionCreateResponse.kt
+++ b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/models/ChatCompletionCreateResponse.kt
@@ -13,7 +13,7 @@ import com.omnistack.api.core.JsonField
 import com.omnistack.api.core.JsonMissing
 import com.omnistack.api.core.JsonValue
 import com.omnistack.api.core.NoAutoDetect
-import com.omnistack.api.core.toUnmodifiable
+import com.omnistack.api.core.toImmutable
 import com.omnistack.api.errors.OmnistackInvalidDataException
 import java.util.Objects
 
@@ -248,14 +248,14 @@ private constructor(
         fun build(): ChatCompletionCreateResponse =
             ChatCompletionCreateResponse(
                 id,
-                choices.map { it.toUnmodifiable() },
+                choices.map { it.toImmutable() },
                 created,
                 model,
                 serviceTier,
                 systemFingerprint,
                 object_,
                 usage,
-                additionalProperties.toUnmodifiable(),
+                additionalProperties.toImmutable(),
             )
     }
 
@@ -411,7 +411,7 @@ private constructor(
                     index,
                     message,
                     logprobs,
-                    additionalProperties.toUnmodifiable(),
+                    additionalProperties.toImmutable(),
                 )
         }
 
@@ -578,9 +578,9 @@ private constructor(
 
                 fun build(): Logprobs =
                     Logprobs(
-                        content.map { it.toUnmodifiable() },
-                        refusal.map { it.toUnmodifiable() },
-                        additionalProperties.toUnmodifiable(),
+                        content.map { it.toImmutable() },
+                        refusal.map { it.toImmutable() },
+                        additionalProperties.toImmutable(),
                     )
             }
 
@@ -766,9 +766,9 @@ private constructor(
                         Content(
                             token,
                             logprob,
-                            bytes.map { it.toUnmodifiable() },
-                            topLogprobs.map { it.toUnmodifiable() },
-                            additionalProperties.toUnmodifiable(),
+                            bytes.map { it.toImmutable() },
+                            topLogprobs.map { it.toImmutable() },
+                            additionalProperties.toImmutable(),
                         )
                 }
 
@@ -920,8 +920,8 @@ private constructor(
                             TopLogprob(
                                 token,
                                 logprob,
-                                bytes.map { it.toUnmodifiable() },
-                                additionalProperties.toUnmodifiable(),
+                                bytes.map { it.toImmutable() },
+                                additionalProperties.toImmutable(),
                             )
                     }
 
@@ -1149,9 +1149,9 @@ private constructor(
                         Refusal(
                             token,
                             logprob,
-                            bytes.map { it.toUnmodifiable() },
-                            topLogprobs.map { it.toUnmodifiable() },
-                            additionalProperties.toUnmodifiable(),
+                            bytes.map { it.toImmutable() },
+                            topLogprobs.map { it.toImmutable() },
+                            additionalProperties.toImmutable(),
                         )
                 }
 
@@ -1303,8 +1303,8 @@ private constructor(
                             TopLogprob(
                                 token,
                                 logprob,
-                                bytes.map { it.toUnmodifiable() },
-                                additionalProperties.toUnmodifiable(),
+                                bytes.map { it.toImmutable() },
+                                additionalProperties.toImmutable(),
                             )
                     }
 
@@ -1532,10 +1532,10 @@ private constructor(
                     Message(
                         content,
                         refusal,
-                        toolCalls.map { it.toUnmodifiable() },
+                        toolCalls.map { it.toImmutable() },
                         role,
                         functionCall,
-                        additionalProperties.toUnmodifiable(),
+                        additionalProperties.toImmutable(),
                     )
             }
 
@@ -1705,7 +1705,7 @@ private constructor(
                         FunctionCall(
                             arguments,
                             name,
-                            additionalProperties.toUnmodifiable(),
+                            additionalProperties.toImmutable(),
                         )
                 }
 
@@ -1838,7 +1838,7 @@ private constructor(
                             id,
                             type,
                             function,
-                            additionalProperties.toUnmodifiable(),
+                            additionalProperties.toImmutable(),
                         )
                 }
 
@@ -1955,7 +1955,7 @@ private constructor(
                             Function(
                                 name,
                                 arguments,
-                                additionalProperties.toUnmodifiable(),
+                                additionalProperties.toImmutable(),
                             )
                     }
 
@@ -2344,7 +2344,7 @@ private constructor(
                     promptTokens,
                     totalTokens,
                     completionTokensDetails,
-                    additionalProperties.toUnmodifiable(),
+                    additionalProperties.toImmutable(),
                 )
         }
 
@@ -2422,7 +2422,7 @@ private constructor(
                     }
 
                 fun build(): CompletionTokensDetails =
-                    CompletionTokensDetails(reasoningTokens, additionalProperties.toUnmodifiable())
+                    CompletionTokensDetails(reasoningTokens, additionalProperties.toImmutable())
             }
 
             override fun equals(other: Any?): Boolean {
diff --git a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/models/CompletionCreateParams.kt b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/models/CompletionCreateParams.kt
index 143c6fb..8117a42 100644
--- a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/models/CompletionCreateParams.kt
+++ b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/models/CompletionCreateParams.kt
@@ -21,7 +21,7 @@ import com.omnistack.api.core.JsonField
 import com.omnistack.api.core.JsonValue
 import com.omnistack.api.core.NoAutoDetect
 import com.omnistack.api.core.getOrThrow
-import com.omnistack.api.core.toUnmodifiable
+import com.omnistack.api.core.toImmutable
 import com.omnistack.api.errors.OmnistackInvalidDataException
 import com.omnistack.api.models.*
 import java.util.Objects
@@ -552,7 +552,7 @@ constructor(
                     temperature,
                     topP,
                     user,
-                    additionalProperties.toUnmodifiable(),
+                    additionalProperties.toImmutable(),
                 )
         }
 
@@ -958,9 +958,9 @@ constructor(
                 temperature,
                 topP,
                 user,
-                additionalQueryParams.mapValues { it.value.toUnmodifiable() }.toUnmodifiable(),
-                additionalHeaders.mapValues { it.value.toUnmodifiable() }.toUnmodifiable(),
-                additionalBodyProperties.toUnmodifiable(),
+                additionalQueryParams.mapValues { it.value.toImmutable() }.toImmutable(),
+                additionalHeaders.mapValues { it.value.toImmutable() }.toImmutable(),
+                additionalBodyProperties.toImmutable(),
             )
     }
 
@@ -1049,6 +1049,7 @@ constructor(
 
             override fun ObjectCodec.deserialize(node: JsonNode): Model {
                 val json = JsonValue.fromJsonNode(node)
+
                 tryDeserialize(node, jacksonTypeRef<String>())?.let {
                     return Model(string = it, _json = json)
                 }
@@ -1251,6 +1252,7 @@ constructor(
 
             override fun ObjectCodec.deserialize(node: JsonNode): Prompt {
                 val json = JsonValue.fromJsonNode(node)
+
                 tryDeserialize(node, jacksonTypeRef<String>())?.let {
                     return Prompt(string = it, _json = json)
                 }
@@ -1340,7 +1342,7 @@ constructor(
                 this.additionalProperties.putAll(additionalProperties)
             }
 
-            fun build(): LogitBias = LogitBias(additionalProperties.toUnmodifiable())
+            fun build(): LogitBias = LogitBias(additionalProperties.toImmutable())
         }
 
         override fun equals(other: Any?): Boolean {
@@ -1448,6 +1450,7 @@ constructor(
 
             override fun ObjectCodec.deserialize(node: JsonNode): Stop {
                 val json = JsonValue.fromJsonNode(node)
+
                 tryDeserialize(node, jacksonTypeRef<String>())?.let {
                     return Stop(string = it, _json = json)
                 }
@@ -1538,7 +1541,7 @@ constructor(
             }
 
             fun build(): StreamOptions =
-                StreamOptions(includeUsage, additionalProperties.toUnmodifiable())
+                StreamOptions(includeUsage, additionalProperties.toImmutable())
         }
 
         override fun equals(other: Any?): Boolean {
diff --git a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/models/CompletionCreateResponse.kt b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/models/CompletionCreateResponse.kt
index eedc362..3bc8592 100644
--- a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/models/CompletionCreateResponse.kt
+++ b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/models/CompletionCreateResponse.kt
@@ -13,7 +13,7 @@ import com.omnistack.api.core.JsonField
 import com.omnistack.api.core.JsonMissing
 import com.omnistack.api.core.JsonValue
 import com.omnistack.api.core.NoAutoDetect
-import com.omnistack.api.core.toUnmodifiable
+import com.omnistack.api.core.toImmutable
 import com.omnistack.api.errors.OmnistackInvalidDataException
 import java.util.Objects
 
@@ -219,13 +219,13 @@ private constructor(
         fun build(): CompletionCreateResponse =
             CompletionCreateResponse(
                 id,
-                choices.map { it.toUnmodifiable() },
+                choices.map { it.toImmutable() },
                 created,
                 model,
                 systemFingerprint,
                 object_,
                 usage,
-                additionalProperties.toUnmodifiable(),
+                additionalProperties.toImmutable(),
             )
     }
 
@@ -365,7 +365,7 @@ private constructor(
                     index,
                     logprobs,
                     text,
-                    additionalProperties.toUnmodifiable(),
+                    additionalProperties.toImmutable(),
                 )
         }
 
@@ -547,11 +547,11 @@ private constructor(
 
                 fun build(): Logprobs =
                     Logprobs(
-                        textOffset.map { it.toUnmodifiable() },
-                        tokenLogprobs.map { it.toUnmodifiable() },
-                        tokens.map { it.toUnmodifiable() },
-                        topLogprobs.map { it.toUnmodifiable() },
-                        additionalProperties.toUnmodifiable(),
+                        textOffset.map { it.toImmutable() },
+                        tokenLogprobs.map { it.toImmutable() },
+                        tokens.map { it.toImmutable() },
+                        topLogprobs.map { it.toImmutable() },
+                        additionalProperties.toImmutable(),
                     )
             }
 
@@ -604,7 +604,7 @@ private constructor(
                             this.additionalProperties.putAll(additionalProperties)
                         }
 
-                    fun build(): TopLogprob = TopLogprob(additionalProperties.toUnmodifiable())
+                    fun build(): TopLogprob = TopLogprob(additionalProperties.toImmutable())
                 }
 
                 override fun equals(other: Any?): Boolean {
@@ -861,7 +861,7 @@ private constructor(
                     promptTokens,
                     totalTokens,
                     completionTokensDetails,
-                    additionalProperties.toUnmodifiable(),
+                    additionalProperties.toImmutable(),
                 )
         }
 
@@ -939,7 +939,7 @@ private constructor(
                     }
 
                 fun build(): CompletionTokensDetails =
-                    CompletionTokensDetails(reasoningTokens, additionalProperties.toUnmodifiable())
+                    CompletionTokensDetails(reasoningTokens, additionalProperties.toImmutable())
             }
 
             override fun equals(other: Any?): Boolean {
diff --git a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/models/ProjectApiKey.kt b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/models/ProjectApiKey.kt
index c98eb85..6bb5b5c 100644
--- a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/models/ProjectApiKey.kt
+++ b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/models/ProjectApiKey.kt
@@ -13,7 +13,7 @@ import com.omnistack.api.core.JsonField
 import com.omnistack.api.core.JsonMissing
 import com.omnistack.api.core.JsonValue
 import com.omnistack.api.core.NoAutoDetect
-import com.omnistack.api.core.toUnmodifiable
+import com.omnistack.api.core.toImmutable
 import com.omnistack.api.errors.OmnistackInvalidDataException
 import java.util.Objects
 
@@ -178,7 +178,7 @@ private constructor(
                 createdAt,
                 id,
                 owner,
-                additionalProperties.toUnmodifiable(),
+                additionalProperties.toImmutable(),
             )
     }
 
@@ -343,7 +343,7 @@ private constructor(
                     type,
                     user,
                     serviceAccount,
-                    additionalProperties.toUnmodifiable(),
+                    additionalProperties.toImmutable(),
                 )
         }
 
diff --git a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/models/ProjectServiceAccount.kt b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/models/ProjectServiceAccount.kt
index 435adb4..bfa8eaa 100644
--- a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/models/ProjectServiceAccount.kt
+++ b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/models/ProjectServiceAccount.kt
@@ -13,7 +13,7 @@ import com.omnistack.api.core.JsonField
 import com.omnistack.api.core.JsonMissing
 import com.omnistack.api.core.JsonValue
 import com.omnistack.api.core.NoAutoDetect
-import com.omnistack.api.core.toUnmodifiable
+import com.omnistack.api.core.toImmutable
 import com.omnistack.api.errors.OmnistackInvalidDataException
 import java.util.Objects
 
@@ -161,7 +161,7 @@ private constructor(
                 name,
                 role,
                 createdAt,
-                additionalProperties.toUnmodifiable(),
+                additionalProperties.toImmutable(),
             )
     }
 
diff --git a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/models/ProjectUser.kt b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/models/ProjectUser.kt
index 8f437eb..fee5e9d 100644
--- a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/models/ProjectUser.kt
+++ b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/models/ProjectUser.kt
@@ -13,7 +13,7 @@ import com.omnistack.api.core.JsonField
 import com.omnistack.api.core.JsonMissing
 import com.omnistack.api.core.JsonValue
 import com.omnistack.api.core.NoAutoDetect
-import com.omnistack.api.core.toUnmodifiable
+import com.omnistack.api.core.toImmutable
 import com.omnistack.api.errors.OmnistackInvalidDataException
 import java.util.Objects
 
@@ -180,7 +180,7 @@ private constructor(
                 email,
                 role,
                 addedAt,
-                additionalProperties.toUnmodifiable(),
+                additionalProperties.toImmutable(),
             )
     }
 
diff --git a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/services/async/ChatServiceAsync.kt b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/services/async/ChatServiceAsync.kt
index bf43aa0..a838633 100644
--- a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/services/async/ChatServiceAsync.kt
+++ b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/services/async/ChatServiceAsync.kt
@@ -1,7 +1,5 @@
 // File generated from our OpenAPI spec by Stainless.
 
-@file:Suppress("OVERLOADS_INTERFACE") // See https://youtrack.jetbrains.com/issue/KT-36102
-
 package com.omnistack.api.services.async
 
 import com.omnistack.api.services.async.chats.CompletionServiceAsync
diff --git a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/services/async/CompletionServiceAsync.kt b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/services/async/CompletionServiceAsync.kt
index 3d9b691..0860331 100644
--- a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/services/async/CompletionServiceAsync.kt
+++ b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/services/async/CompletionServiceAsync.kt
@@ -1,7 +1,5 @@
 // File generated from our OpenAPI spec by Stainless.
 
-@file:Suppress("OVERLOADS_INTERFACE") // See https://youtrack.jetbrains.com/issue/KT-36102
-
 package com.omnistack.api.services.async
 
 import com.omnistack.api.core.RequestOptions
diff --git a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/services/async/chats/CompletionServiceAsync.kt b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/services/async/chats/CompletionServiceAsync.kt
index 8c73ac5..549848a 100644
--- a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/services/async/chats/CompletionServiceAsync.kt
+++ b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/services/async/chats/CompletionServiceAsync.kt
@@ -1,7 +1,5 @@
 // File generated from our OpenAPI spec by Stainless.
 
-@file:Suppress("OVERLOADS_INTERFACE") // See https://youtrack.jetbrains.com/issue/KT-36102
-
 package com.omnistack.api.services.async.chats
 
 import com.omnistack.api.core.RequestOptions
diff --git a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/services/blocking/ChatService.kt b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/services/blocking/ChatService.kt
index 0e27c52..76833bd 100644
--- a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/services/blocking/ChatService.kt
+++ b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/services/blocking/ChatService.kt
@@ -1,7 +1,5 @@
 // File generated from our OpenAPI spec by Stainless.
 
-@file:Suppress("OVERLOADS_INTERFACE") // See https://youtrack.jetbrains.com/issue/KT-36102
-
 package com.omnistack.api.services.blocking
 
 import com.omnistack.api.services.blocking.chats.CompletionService
diff --git a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/services/blocking/CompletionService.kt b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/services/blocking/CompletionService.kt
index 66db2c0..58f07cb 100644
--- a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/services/blocking/CompletionService.kt
+++ b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/services/blocking/CompletionService.kt
@@ -1,7 +1,5 @@
 // File generated from our OpenAPI spec by Stainless.
 
-@file:Suppress("OVERLOADS_INTERFACE") // See https://youtrack.jetbrains.com/issue/KT-36102
-
 package com.omnistack.api.services.blocking
 
 import com.omnistack.api.core.RequestOptions
diff --git a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/services/blocking/chats/CompletionService.kt b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/services/blocking/chats/CompletionService.kt
index 43728d2..1dfe901 100644
--- a/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/services/blocking/chats/CompletionService.kt
+++ b/omnistack-kotlin-core/src/main/kotlin/com/omnistack/api/services/blocking/chats/CompletionService.kt
@@ -1,7 +1,5 @@
 // File generated from our OpenAPI spec by Stainless.
 
-@file:Suppress("OVERLOADS_INTERFACE") // See https://youtrack.jetbrains.com/issue/KT-36102
-
 package com.omnistack.api.services.blocking.chats
 
 import com.omnistack.api.core.RequestOptions
diff --git a/omnistack-kotlin-core/src/test/kotlin/com/omnistack/api/core/PhantomReachableTest.kt b/omnistack-kotlin-core/src/test/kotlin/com/omnistack/api/core/PhantomReachableTest.kt
new file mode 100644
index 0000000..8205cdf
--- /dev/null
+++ b/omnistack-kotlin-core/src/test/kotlin/com/omnistack/api/core/PhantomReachableTest.kt
@@ -0,0 +1,27 @@
+package com.omnistack.api.core
+
+import org.assertj.core.api.Assertions.assertThat
+import org.junit.jupiter.api.Test
+
+internal class PhantomReachableTest {
+
+    @Test
+    fun closeWhenPhantomReachable_whenObservedIsGarbageCollected_closesCloseable() {
+        var closed = false
+        val closeable = AutoCloseable { closed = true }
+
+        closeWhenPhantomReachable(
+            // Pass an inline object for the object to observe so that it becomes immediately
+            // unreachable.
+            Any(),
+            closeable
+        )
+
+        assertThat(closed).isFalse()
+
+        System.gc()
+        Thread.sleep(3000)
+
+        assertThat(closed).isTrue()
+    }
+}
diff --git a/omnistack-kotlin-core/src/test/kotlin/com/omnistack/api/core/http/HeadersTest.kt b/omnistack-kotlin-core/src/test/kotlin/com/omnistack/api/core/http/HeadersTest.kt
new file mode 100644
index 0000000..71b7df2
--- /dev/null
+++ b/omnistack-kotlin-core/src/test/kotlin/com/omnistack/api/core/http/HeadersTest.kt
@@ -0,0 +1,274 @@
+package com.omnistack.api.core.http
+
+import org.assertj.core.api.Assertions.assertThat
+import org.assertj.core.api.Assertions.catchThrowable
+import org.assertj.core.api.Assumptions.assumeThat
+import org.junit.jupiter.params.ParameterizedTest
+import org.junit.jupiter.params.provider.EnumSource
+
+internal class HeadersTest {
+
+    enum class TestCase(
+        val headers: Headers,
+        val expectedMap: Map<String, List<String>>,
+        val expectedSize: Int
+    ) {
+        EMPTY(Headers.builder().build(), expectedMap = mapOf(), expectedSize = 0),
+        PUT_ONE(
+            Headers.builder().put("name", "value").build(),
+            expectedMap = mapOf("name" to listOf("value")),
+            expectedSize = 1
+        ),
+        PUT_MULTIPLE(
+            Headers.builder().put("name", listOf("value1", "value2")).build(),
+            expectedMap = mapOf("name" to listOf("value1", "value2")),
+            expectedSize = 2
+        ),
+        MULTIPLE_PUT(
+            Headers.builder().put("name1", "value").put("name2", "value").build(),
+            expectedMap = mapOf("name1" to listOf("value"), "name2" to listOf("value")),
+            expectedSize = 2
+        ),
+        MULTIPLE_PUT_SAME_NAME(
+            Headers.builder().put("name", "value1").put("name", "value2").build(),
+            expectedMap = mapOf("name" to listOf("value1", "value2")),
+            expectedSize = 2
+        ),
+        MULTIPLE_PUT_MULTIPLE(
+            Headers.builder()
+                .put("name", listOf("value1", "value2"))
+                .put("name", listOf("value1", "value2"))
+                .build(),
+            expectedMap = mapOf("name" to listOf("value1", "value2", "value1", "value2")),
+            expectedSize = 4
+        ),
+        PUT_CASE_INSENSITIVE(
+            Headers.builder()
+                .put("name", "value1")
+                .put("NAME", "value2")
+                .put("nAmE", "value3")
+                .build(),
+            expectedMap = mapOf("name" to listOf("value1", "value2", "value3")),
+            expectedSize = 3
+        ),
+        PUT_ALL_MAP(
+            Headers.builder()
+                .putAll(
+                    mapOf(
+                        "name1" to listOf("value1", "value2"),
+                        "name2" to listOf("value1", "value2")
+                    )
+                )
+                .build(),
+            expectedMap =
+                mapOf("name1" to listOf("value1", "value2"), "name2" to listOf("value1", "value2")),
+            expectedSize = 4
+        ),
+        PUT_ALL_HEADERS(
+            Headers.builder().putAll(Headers.builder().put("name", "value").build()).build(),
+            expectedMap = mapOf("name" to listOf("value")),
+            expectedSize = 1
+        ),
+        PUT_ALL_CASE_INSENSITIVE(
+            Headers.builder()
+                .putAll(
+                    mapOf(
+                        "name" to listOf("value1"),
+                        "NAME" to listOf("value2"),
+                        "nAmE" to listOf("value3")
+                    )
+                )
+                .build(),
+            expectedMap = mapOf("name" to listOf("value1", "value2", "value3")),
+            expectedSize = 3
+        ),
+        REMOVE_ABSENT(
+            Headers.builder().remove("name").build(),
+            expectedMap = mapOf(),
+            expectedSize = 0
+        ),
+        REMOVE_PRESENT_ONE(
+            Headers.builder().put("name", "value").remove("name").build(),
+            expectedMap = mapOf(),
+            expectedSize = 0
+        ),
+        REMOVE_PRESENT_MULTIPLE(
+            Headers.builder().put("name", listOf("value1", "value2")).remove("name").build(),
+            expectedMap = mapOf(),
+            expectedSize = 0
+        ),
+        REMOVE_CASE_INSENSITIVE(
+            Headers.builder().put("name", listOf("value1", "value2")).remove("NAME").build(),
+            expectedMap = mapOf(),
+            expectedSize = 0
+        ),
+        REMOVE_ALL(
+            Headers.builder()
+                .put("name1", "value")
+                .put("name3", "value")
+                .removeAll(setOf("name1", "name2", "name3"))
+                .build(),
+            expectedMap = mapOf(),
+            expectedSize = 0
+        ),
+        REMOVE_ALL_CASE_INSENSITIVE(
+            Headers.builder()
+                .put("name1", "value")
+                .put("name3", "value")
+                .removeAll(setOf("NAME1", "nAmE3"))
+                .build(),
+            expectedMap = mapOf(),
+            expectedSize = 0
+        ),
+        CLEAR(
+            Headers.builder().put("name1", "value").put("name2", "value").clear().build(),
+            expectedMap = mapOf(),
+            expectedSize = 0
+        ),
+        REPLACE_ONE_ABSENT(
+            Headers.builder().replace("name", "value").build(),
+            expectedMap = mapOf("name" to listOf("value")),
+            expectedSize = 1
+        ),
+        REPLACE_ONE_PRESENT_ONE(
+            Headers.builder().put("name", "value1").replace("name", "value2").build(),
+            expectedMap = mapOf("name" to listOf("value2")),
+            expectedSize = 1
+        ),
+        REPLACE_ONE_PRESENT_MULTIPLE(
+            Headers.builder()
+                .put("name", listOf("value1", "value2"))
+                .replace("name", "value3")
+                .build(),
+            expectedMap = mapOf("name" to listOf("value3")),
+            expectedSize = 1
+        ),
+        REPLACE_MULTIPLE_ABSENT(
+            Headers.builder().replace("name", listOf("value1", "value2")).build(),
+            expectedMap = mapOf("name" to listOf("value1", "value2")),
+            expectedSize = 2
+        ),
+        REPLACE_MULTIPLE_PRESENT_ONE(
+            Headers.builder()
+                .put("name", "value1")
+                .replace("name", listOf("value2", "value3"))
+                .build(),
+            expectedMap = mapOf("name" to listOf("value2", "value3")),
+            expectedSize = 2
+        ),
+        REPLACE_MULTIPLE_PRESENT_MULTIPLE(
+            Headers.builder()
+                .put("name", listOf("value1", "value2"))
+                .replace("name", listOf("value3", "value4"))
+                .build(),
+            expectedMap = mapOf("name" to listOf("value3", "value4")),
+            expectedSize = 2
+        ),
+        REPLACE_CASE_INSENSITIVE(
+            Headers.builder()
+                .put("name", "value1")
+                .replace("NAME", listOf("value2", "value3"))
+                .build(),
+            expectedMap = mapOf("NAME" to listOf("value2", "value3")),
+            expectedSize = 2
+        ),
+        REPLACE_ALL_MAP(
+            Headers.builder()
+                .put("name1", "value1")
+                .put("name2", "value1")
+                .put("name3", "value1")
+                .replaceAll(mapOf("name1" to listOf("value2"), "name3" to listOf("value2")))
+                .build(),
+            expectedMap =
+                mapOf(
+                    "name1" to listOf("value2"),
+                    "name2" to listOf("value1"),
+                    "name3" to listOf("value2")
+                ),
+            expectedSize = 3
+        ),
+        REPLACE_ALL_HEADERS(
+            Headers.builder()
+                .put("name1", "value1")
+                .put("name2", "value1")
+                .put("name3", "value1")
+                .replaceAll(Headers.builder().put("name1", "value2").put("name3", "value2").build())
+                .build(),
+            expectedMap =
+                mapOf(
+                    "name1" to listOf("value2"),
+                    "name2" to listOf("value1"),
+                    "name3" to listOf("value2")
+                ),
+            expectedSize = 3
+        ),
+        REPLACE_ALL_CASE_INSENSITIVE(
+            Headers.builder()
+                .put("name1", "value1")
+                .put("name2", "value1")
+                .replaceAll(mapOf("NAME1" to listOf("value2"), "nAmE2" to listOf("value2")))
+                .build(),
+            expectedMap = mapOf("NAME1" to listOf("value2"), "nAmE2" to listOf("value2")),
+            expectedSize = 2
+        )
+    }
+
+    @ParameterizedTest
+    @EnumSource
+    fun namesAndValues(testCase: TestCase) {
+        val map = mutableMapOf<String, List<String>>()
+        val headers = testCase.headers
+        headers.names().forEach { name -> map[name] = headers.values(name) }
+
+        assertThat(map).isEqualTo(testCase.expectedMap)
+    }
+
+    @ParameterizedTest
+    @EnumSource
+    fun caseInsensitiveNames(testCase: TestCase) {
+        val headers = testCase.headers
+
+        for (name in headers.names()) {
+            assertThat(headers.values(name)).isEqualTo(headers.values(name.lowercase()))
+            assertThat(headers.values(name)).isEqualTo(headers.values(name.uppercase()))
+        }
+    }
+
+    @ParameterizedTest
+    @EnumSource
+    fun size(testCase: TestCase) {
+        val size = testCase.headers.size
+
+        assertThat(size).isEqualTo(testCase.expectedSize)
+    }
+
+    @ParameterizedTest
+    @EnumSource
+    fun namesAreImmutable(testCase: TestCase) {
+        val headers = testCase.headers
+        val headerNamesCopy = headers.names().toSet()
+
+        val throwable = catchThrowable {
+            (headers.names() as MutableSet<String>).add("another name")
+        }
+
+        assertThat(throwable).isInstanceOf(UnsupportedOperationException::class.java)
+        assertThat(headers.names()).isEqualTo(headerNamesCopy)
+    }
+
+    @ParameterizedTest
+    @EnumSource
+    fun valuesAreImmutable(testCase: TestCase) {
+        val headers = testCase.headers
+        assumeThat(headers.size).isNotEqualTo(0)
+        val name = headers.names().first()
+        val headerValuesCopy = headers.values(name).toList()
+
+        val throwable = catchThrowable {
+            (headers.values(name) as MutableList<String>).add("another value")
+        }
+
+        assertThat(throwable).isInstanceOf(UnsupportedOperationException::class.java)
+        assertThat(headers.values(name)).isEqualTo(headerValuesCopy)
+    }
+}
diff --git a/omnistack-kotlin-core/src/test/kotlin/com/omnistack/api/core/http/QueryParamsTest.kt b/omnistack-kotlin-core/src/test/kotlin/com/omnistack/api/core/http/QueryParamsTest.kt
new file mode 100644
index 0000000..7c0a8a6
--- /dev/null
+++ b/omnistack-kotlin-core/src/test/kotlin/com/omnistack/api/core/http/QueryParamsTest.kt
@@ -0,0 +1,212 @@
+package com.omnistack.api.core.http
+
+import org.assertj.core.api.Assertions.assertThat
+import org.assertj.core.api.Assertions.catchThrowable
+import org.assertj.core.api.Assumptions.assumeThat
+import org.junit.jupiter.params.ParameterizedTest
+import org.junit.jupiter.params.provider.EnumSource
+
+internal class QueryParamsTest {
+
+    enum class TestCase(
+        val queryParams: QueryParams,
+        val expectedMap: Map<String, List<String>>,
+        val expectedSize: Int
+    ) {
+        EMPTY(QueryParams.builder().build(), expectedMap = mapOf(), expectedSize = 0),
+        PUT_ONE(
+            QueryParams.builder().put("key", "value").build(),
+            expectedMap = mapOf("key" to listOf("value")),
+            expectedSize = 1
+        ),
+        PUT_MULTIPLE(
+            QueryParams.builder().put("key", listOf("value1", "value2")).build(),
+            expectedMap = mapOf("key" to listOf("value1", "value2")),
+            expectedSize = 2
+        ),
+        MULTIPLE_PUT(
+            QueryParams.builder().put("key1", "value").put("key2", "value").build(),
+            expectedMap = mapOf("key1" to listOf("value"), "key2" to listOf("value")),
+            expectedSize = 2
+        ),
+        MULTIPLE_PUT_SAME_NAME(
+            QueryParams.builder().put("key", "value1").put("key", "value2").build(),
+            expectedMap = mapOf("key" to listOf("value1", "value2")),
+            expectedSize = 2
+        ),
+        MULTIPLE_PUT_MULTIPLE(
+            QueryParams.builder()
+                .put("key", listOf("value1", "value2"))
+                .put("key", listOf("value1", "value2"))
+                .build(),
+            expectedMap = mapOf("key" to listOf("value1", "value2", "value1", "value2")),
+            expectedSize = 4
+        ),
+        PUT_ALL_MAP(
+            QueryParams.builder()
+                .putAll(
+                    mapOf(
+                        "key1" to listOf("value1", "value2"),
+                        "key2" to listOf("value1", "value2")
+                    )
+                )
+                .build(),
+            expectedMap =
+                mapOf("key1" to listOf("value1", "value2"), "key2" to listOf("value1", "value2")),
+            expectedSize = 4
+        ),
+        PUT_ALL_HEADERS(
+            QueryParams.builder().putAll(QueryParams.builder().put("key", "value").build()).build(),
+            expectedMap = mapOf("key" to listOf("value")),
+            expectedSize = 1
+        ),
+        REMOVE_ABSENT(
+            QueryParams.builder().remove("key").build(),
+            expectedMap = mapOf(),
+            expectedSize = 0
+        ),
+        REMOVE_PRESENT_ONE(
+            QueryParams.builder().put("key", "value").remove("key").build(),
+            expectedMap = mapOf(),
+            expectedSize = 0
+        ),
+        REMOVE_PRESENT_MULTIPLE(
+            QueryParams.builder().put("key", listOf("value1", "value2")).remove("key").build(),
+            expectedMap = mapOf(),
+            expectedSize = 0
+        ),
+        REMOVE_ALL(
+            QueryParams.builder()
+                .put("key1", "value")
+                .put("key3", "value")
+                .removeAll(setOf("key1", "key2", "key3"))
+                .build(),
+            expectedMap = mapOf(),
+            expectedSize = 0
+        ),
+        CLEAR(
+            QueryParams.builder().put("key1", "value").put("key2", "value").clear().build(),
+            expectedMap = mapOf(),
+            expectedSize = 0
+        ),
+        REPLACE_ONE_ABSENT(
+            QueryParams.builder().replace("key", "value").build(),
+            expectedMap = mapOf("key" to listOf("value")),
+            expectedSize = 1
+        ),
+        REPLACE_ONE_PRESENT_ONE(
+            QueryParams.builder().put("key", "value1").replace("key", "value2").build(),
+            expectedMap = mapOf("key" to listOf("value2")),
+            expectedSize = 1
+        ),
+        REPLACE_ONE_PRESENT_MULTIPLE(
+            QueryParams.builder()
+                .put("key", listOf("value1", "value2"))
+                .replace("key", "value3")
+                .build(),
+            expectedMap = mapOf("key" to listOf("value3")),
+            expectedSize = 1
+        ),
+        REPLACE_MULTIPLE_ABSENT(
+            QueryParams.builder().replace("key", listOf("value1", "value2")).build(),
+            expectedMap = mapOf("key" to listOf("value1", "value2")),
+            expectedSize = 2
+        ),
+        REPLACE_MULTIPLE_PRESENT_ONE(
+            QueryParams.builder()
+                .put("key", "value1")
+                .replace("key", listOf("value2", "value3"))
+                .build(),
+            expectedMap = mapOf("key" to listOf("value2", "value3")),
+            expectedSize = 2
+        ),
+        REPLACE_MULTIPLE_PRESENT_MULTIPLE(
+            QueryParams.builder()
+                .put("key", listOf("value1", "value2"))
+                .replace("key", listOf("value3", "value4"))
+                .build(),
+            expectedMap = mapOf("key" to listOf("value3", "value4")),
+            expectedSize = 2
+        ),
+        REPLACE_ALL_MAP(
+            QueryParams.builder()
+                .put("key1", "value1")
+                .put("key2", "value1")
+                .put("key3", "value1")
+                .replaceAll(mapOf("key1" to listOf("value2"), "key3" to listOf("value2")))
+                .build(),
+            expectedMap =
+                mapOf(
+                    "key1" to listOf("value2"),
+                    "key2" to listOf("value1"),
+                    "key3" to listOf("value2")
+                ),
+            expectedSize = 3
+        ),
+        REPLACE_ALL_HEADERS(
+            QueryParams.builder()
+                .put("key1", "value1")
+                .put("key2", "value1")
+                .put("key3", "value1")
+                .replaceAll(
+                    QueryParams.builder().put("key1", "value2").put("key3", "value2").build()
+                )
+                .build(),
+            expectedMap =
+                mapOf(
+                    "key1" to listOf("value2"),
+                    "key2" to listOf("value1"),
+                    "key3" to listOf("value2")
+                ),
+            expectedSize = 3
+        )
+    }
+
+    @ParameterizedTest
+    @EnumSource
+    fun keysAndValues(testCase: TestCase) {
+        val map = mutableMapOf<String, List<String>>()
+        val queryParams = testCase.queryParams
+        queryParams.keys().forEach { key -> map[key] = queryParams.values(key) }
+
+        assertThat(map).isEqualTo(testCase.expectedMap)
+    }
+
+    @ParameterizedTest
+    @EnumSource
+    fun size(testCase: TestCase) {
+        val size = testCase.queryParams.size
+
+        assertThat(size).isEqualTo(testCase.expectedSize)
+    }
+
+    @ParameterizedTest
+    @EnumSource
+    fun keysAreImmutable(testCase: TestCase) {
+        val queryParams = testCase.queryParams
+        val queryParamKeysCopy = queryParams.keys().toSet()
+
+        val throwable = catchThrowable {
+            (queryParams.keys() as MutableSet<String>).add("another key")
+        }
+
+        assertThat(throwable).isInstanceOf(UnsupportedOperationException::class.java)
+        assertThat(queryParams.keys()).isEqualTo(queryParamKeysCopy)
+    }
+
+    @ParameterizedTest
+    @EnumSource
+    fun valuesAreImmutable(testCase: TestCase) {
+        val queryParams = testCase.queryParams
+        assumeThat(queryParams.size).isNotEqualTo(0)
+        val key = queryParams.keys().first()
+        val queryParamValuesCopy = queryParams.values(key).toList()
+
+        val throwable = catchThrowable {
+            (queryParams.values(key) as MutableList<String>).add("another value")
+        }
+
+        assertThat(throwable).isInstanceOf(UnsupportedOperationException::class.java)
+        assertThat(queryParams.values(key)).isEqualTo(queryParamValuesCopy)
+    }
+}
diff --git a/omnistack-kotlin-core/src/test/kotlin/com/omnistack/api/core/http/SerializerTest.kt b/omnistack-kotlin-core/src/test/kotlin/com/omnistack/api/core/http/SerializerTest.kt
index c1653f5..588c244 100644
--- a/omnistack-kotlin-core/src/test/kotlin/com/omnistack/api/core/http/SerializerTest.kt
+++ b/omnistack-kotlin-core/src/test/kotlin/com/omnistack/api/core/http/SerializerTest.kt
@@ -92,7 +92,7 @@ internal class SerializerTest {
             fun build(): ClassWithBooleanFieldPrefixedWithIs =
                 ClassWithBooleanFieldPrefixedWithIs(
                     isActive,
-                    additionalProperties.toUnmodifiable(),
+                    additionalProperties.toImmutable(),
                 )
         }
     }
diff --git a/omnistack-kotlin-core/src/test/kotlin/com/omnistack/api/services/blocking/ChatServiceTest.kt b/omnistack-kotlin-core/src/test/kotlin/com/omnistack/api/services/blocking/ChatServiceTest.kt
deleted file mode 100644
index 7fffa08..0000000
--- a/omnistack-kotlin-core/src/test/kotlin/com/omnistack/api/services/blocking/ChatServiceTest.kt
+++ /dev/null
@@ -1,9 +0,0 @@
-// File generated from our OpenAPI spec by Stainless.
-
-package com.omnistack.api.services.blocking
-
-import com.omnistack.api.TestServerExtension
-import com.omnistack.api.models.*
-import org.junit.jupiter.api.extension.ExtendWith
-
-@ExtendWith(TestServerExtension::class) class ChatServiceTest