diff --git a/flipt-java/src/main/java/example/Main.java b/flipt-java/src/main/java/example/Main.java
index 1444a29..b94bb97 100644
--- a/flipt-java/src/main/java/example/Main.java
+++ b/flipt-java/src/main/java/example/Main.java
@@ -12,11 +12,11 @@ public static void main(String[] args) {
     context.put("fizz", "buzz");
 
     EvaluationRequest variantEvaluationRequest =
-        new EvaluationRequest("default", "flag1", "entity", context);
+        new EvaluationRequest("default", "flag1", "entity", context, Optional.empty());
     EvaluationRequest booleanEvaluationRequest =
-        new EvaluationRequest("default", "flag_boolean", "entity", context);
+        new EvaluationRequest("default", "flag_boolean", "entity", context, Optional.empty());
     EvaluationRequest errorEvaluationRequest =
-        new EvaluationRequest("default", "flag1234", "entity", new HashMap<>());
+        new EvaluationRequest("default", "flag1234", "entity", new HashMap<>(), Optional.empty());
 
     List<EvaluationRequest> evaluationRequests = new ArrayList<>();
     evaluationRequests.add(variantEvaluationRequest);
@@ -31,6 +31,7 @@ public static void main(String[] args) {
     BatchEvaluationResponse batchEvaluationResponse =
         fliptClient
             .evaluation()
-            .batch(new BatchEvaluationRequest(Optional.of(""), evaluationRequests));
+            .batch(
+                new BatchEvaluationRequest(Optional.of(""), evaluationRequests, Optional.empty()));
   }
 }
diff --git a/flipt-java/src/main/java/io/flipt/api/evaluation/models/BatchEvaluationRequest.java b/flipt-java/src/main/java/io/flipt/api/evaluation/models/BatchEvaluationRequest.java
index 7e76265..8c0418d 100644
--- a/flipt-java/src/main/java/io/flipt/api/evaluation/models/BatchEvaluationRequest.java
+++ b/flipt-java/src/main/java/io/flipt/api/evaluation/models/BatchEvaluationRequest.java
@@ -9,10 +9,13 @@
 public class BatchEvaluationRequest {
   private final Optional<String> requestId;
   private final List<EvaluationRequest> requests;
+  private Optional<String> reference;
 
-  public BatchEvaluationRequest(Optional<String> requestId, List<EvaluationRequest> requests) {
+  public BatchEvaluationRequest(
+      Optional<String> requestId, List<EvaluationRequest> requests, Optional<String> reference) {
     this.requestId = requestId;
     this.requests = requests;
+    this.reference = reference;
   }
 
   @JsonProperty("requests")
@@ -24,4 +27,9 @@ public List<EvaluationRequest> getRequests() {
   public Optional<String> getRequestId() {
     return requestId;
   }
+
+  @JsonProperty("reference")
+  public Optional<String> getReference() {
+    return reference;
+  }
 }
diff --git a/flipt-java/src/main/java/io/flipt/api/evaluation/models/EvaluationRequest.java b/flipt-java/src/main/java/io/flipt/api/evaluation/models/EvaluationRequest.java
index b572106..6b14bf9 100644
--- a/flipt-java/src/main/java/io/flipt/api/evaluation/models/EvaluationRequest.java
+++ b/flipt-java/src/main/java/io/flipt/api/evaluation/models/EvaluationRequest.java
@@ -3,6 +3,7 @@
 import com.fasterxml.jackson.annotation.JsonInclude;
 import com.fasterxml.jackson.annotation.JsonProperty;
 import java.util.Map;
+import java.util.Optional;
 
 @JsonInclude(JsonInclude.Include.NON_EMPTY)
 public class EvaluationRequest {
@@ -10,13 +11,19 @@ public class EvaluationRequest {
   private final String flagKey;
   private final String entityId;
   private final Map<String, String> context;
+  private final Optional<String> reference;
 
   public EvaluationRequest(
-      String namespaceKey, String flagKey, String entityId, Map<String, String> context) {
+      String namespaceKey,
+      String flagKey,
+      String entityId,
+      Map<String, String> context,
+      Optional<String> reference) {
     this.namespaceKey = namespaceKey;
     this.flagKey = flagKey;
     this.entityId = entityId;
     this.context = context;
+    this.reference = reference;
   }
 
   @JsonProperty("namespaceKey")
@@ -38,4 +45,9 @@ public String getEntityId() {
   public Map<String, String> getContext() {
     return context;
   }
+
+  @JsonProperty("reference")
+  public Optional<String> getReference() {
+    return reference;
+  }
 }
diff --git a/flipt-java/src/test/java/TestFliptClient.java b/flipt-java/src/test/java/TestFliptClient.java
index f7f0c3d..0c459ea 100644
--- a/flipt-java/src/test/java/TestFliptClient.java
+++ b/flipt-java/src/test/java/TestFliptClient.java
@@ -12,8 +12,8 @@ void testVariant() {
     String fliptURL = System.getenv().get("FLIPT_URL");
     String authToken = System.getenv().get("FLIPT_AUTH_TOKEN");
 
-    assert !fliptURL.isEmpty();
-    assert !authToken.isEmpty();
+    assert fliptURL != null && !fliptURL.isEmpty();
+    assert authToken != null && !authToken.isEmpty();
 
     AuthenticationStrategy authenticationStrategy =
         new ClientTokenAuthenticationStrategy(authToken);
@@ -24,7 +24,9 @@ void testVariant() {
     Map<String, String> context = new HashMap<>();
     context.put("fizz", "buzz");
     VariantEvaluationResponse variant =
-        fc.evaluation().variant(new EvaluationRequest("default", "flag1", "entity", context));
+        fc.evaluation()
+            .variant(
+                new EvaluationRequest("default", "flag1", "entity", context, Optional.empty()));
 
     Assertions.assertTrue(variant.isMatch());
     Assertions.assertEquals("flag1", variant.getFlagKey());
@@ -38,8 +40,8 @@ void testBoolean() {
     String fliptURL = System.getenv().get("FLIPT_URL");
     String authToken = System.getenv().get("FLIPT_AUTH_TOKEN");
 
-    assert !fliptURL.isEmpty();
-    assert !authToken.isEmpty();
+    assert fliptURL != null && !fliptURL.isEmpty();
+    assert authToken != null && !authToken.isEmpty();
 
     AuthenticationStrategy authenticationStrategy =
         new ClientTokenAuthenticationStrategy(authToken);
@@ -52,7 +54,9 @@ void testBoolean() {
 
     BooleanEvaluationResponse booleanEvaluation =
         fc.evaluation()
-            .booleanEvaluation(new EvaluationRequest("default", "flag_boolean", "entity", context));
+            .booleanEvaluation(
+                new EvaluationRequest(
+                    "default", "flag_boolean", "entity", context, Optional.empty()));
 
     Assertions.assertTrue(booleanEvaluation.isEnabled());
     Assertions.assertEquals("flag_boolean", booleanEvaluation.getFlagKey());
@@ -64,8 +68,8 @@ void testBatch() {
     String fliptURL = System.getenv().get("FLIPT_URL");
     String authToken = System.getenv().get("FLIPT_AUTH_TOKEN");
 
-    assert !fliptURL.isEmpty();
-    assert !authToken.isEmpty();
+    assert fliptURL != null && !fliptURL.isEmpty();
+    assert authToken != null && !authToken.isEmpty();
 
     AuthenticationStrategy authenticationStrategy =
         new ClientTokenAuthenticationStrategy(authToken);
@@ -77,11 +81,11 @@ void testBatch() {
     context.put("fizz", "buzz");
 
     EvaluationRequest variantEvaluationRequest =
-        new EvaluationRequest("default", "flag1", "entity", context);
+        new EvaluationRequest("default", "flag1", "entity", context, Optional.empty());
     EvaluationRequest booleanEvaluationRequest =
-        new EvaluationRequest("default", "flag_boolean", "entity", context);
+        new EvaluationRequest("default", "flag_boolean", "entity", context, Optional.empty());
     EvaluationRequest errorEvaluationRequest =
-        new EvaluationRequest("default", "flag1234", "entity", new HashMap<>());
+        new EvaluationRequest("default", "flag1234", "entity", new HashMap<>(), Optional.empty());
 
     List<EvaluationRequest> evaluationRequests = new ArrayList<>();
     evaluationRequests.add(variantEvaluationRequest);
@@ -89,7 +93,9 @@ void testBatch() {
     evaluationRequests.add(errorEvaluationRequest);
 
     BatchEvaluationResponse batch =
-        fc.evaluation().batch(new BatchEvaluationRequest(Optional.of(""), evaluationRequests));
+        fc.evaluation()
+            .batch(
+                new BatchEvaluationRequest(Optional.of(""), evaluationRequests, Optional.empty()));
 
     // Variant
     EvaluationResponse first = batch.getResponses().get(0);
diff --git a/flipt-node/src/evaluation/models.ts b/flipt-node/src/evaluation/models.ts
index 849b274..553f3f4 100644
--- a/flipt-node/src/evaluation/models.ts
+++ b/flipt-node/src/evaluation/models.ts
@@ -3,6 +3,7 @@ export interface EvaluationRequest {
   flagKey: string;
   entityId: string;
   context: object;
+  reference?: string;
 }
 
 export interface VariantEvaluationResponse {
@@ -27,6 +28,7 @@ export interface BooleanEvaluationResponse {
 export interface BatchEvaluationRequest {
   request_id?: string;
   requests: EvaluationRequest[];
+  reference?: string;
 }
 
 interface ErrorEvaluationResponse {
diff --git a/flipt-php/src/Flipt/Client/FliptClient.php b/flipt-php/src/Flipt/Client/FliptClient.php
index 5cd9c06..140f870 100644
--- a/flipt-php/src/Flipt/Client/FliptClient.php
+++ b/flipt-php/src/Flipt/Client/FliptClient.php
@@ -31,9 +31,9 @@ public function __construct(string|Client $host, string $namespace = "default",
     /**
      * Returns the boolean evaluation result
      */
-    public function boolean(string $name, $context = [], $entityId = NULL): BooleanEvaluationResult
+    public function boolean(string $name, $context = [], $entityId = NULL, $reference = ""): BooleanEvaluationResult
     {
-        $response = $this->apiRequest('/evaluate/v1/boolean', $this->mergeRequestParams($name, $context, $entityId));
+        $response = $this->apiRequest('/evaluate/v1/boolean', $this->mergeRequestParams($name, $context, $entityId, $reference));
         return new DefaultBooleanEvaluationResult($response['flagKey'], $response['enabled'], $response['reason'], $response['requestDurationMillis'], $response['requestId'], $response['timestamp']);
     }
 
@@ -42,9 +42,9 @@ public function boolean(string $name, $context = [], $entityId = NULL): BooleanE
     /**
      * Returns the variant evaluation result
      */
-    public function variant(string $name, $context = [], $entityId = NULL): VariantEvaluationResult
+    public function variant(string $name, $context = [], $entityId = NULL, $reference = ""): VariantEvaluationResult
     {
-        $response = $this->apiRequest('/evaluate/v1/variant', $this->mergeRequestParams($name, $context, $entityId));
+        $response = $this->apiRequest('/evaluate/v1/variant', $this->mergeRequestParams($name, $context, $entityId, $reference));
         return new DefaultVariantEvaluationResult($response['flagKey'], $response['match'], $response['reason'], $response['requestDurationMillis'], $response['requestId'], $response['timestamp'], $response['segmentKeys'], $response['variantKey'], $response['variantAttachment']);
     }
 
@@ -52,13 +52,14 @@ public function variant(string $name, $context = [], $entityId = NULL): VariantE
     /**
      * Batch return evaluation requests
      */
-    public function batch(array $names, $context = [], $entityId = NULL): array
+    public function batch(array $names, $context = [], $entityId = NULL, $reference = ""): array
     {
 
         $response = $this->apiRequest('/evaluate/v1/batch', [
             'requests' => array_map(function ($name) use ($context, $entityId) {
                 return $this->mergeRequestParams($name, $context, $entityId);
-            }, $names)
+            }, $names),
+            'reference' => $reference
         ]);
 
 
@@ -82,13 +83,14 @@ public function batch(array $names, $context = [], $entityId = NULL): array
     }
 
 
-    protected function mergeRequestParams(string $name, $context = [], $entityId = NULL)
+    protected function mergeRequestParams(string $name, $context = [], $entityId = NULL, $reference = "")
     {
         return [
             'context' => array_merge($this->context, $context),
             'entityId' => isset($entityId) ? $entityId : $this->entityId,
             'flagKey' => $name,
             'namespaceKey' => $this->namespace,
+            'reference' => $this->reference,
         ];
     }
 
diff --git a/flipt-python/flipt/evaluation/models.py b/flipt-python/flipt/evaluation/models.py
index e083fd7..79514ae 100644
--- a/flipt-python/flipt/evaluation/models.py
+++ b/flipt-python/flipt/evaluation/models.py
@@ -26,11 +26,13 @@ class EvaluationRequest(BaseModel):
     flag_key: str
     entity_id: str
     context: dict
+    reference: Optional[str] = None
 
 
 class BatchEvaluationRequest(BaseModel):
     request_id: Optional[str] = None
     requests: List[EvaluationRequest]
+    reference: Optional[str] = None
 
 
 class VariantEvaluationResponse(BaseModel):
@@ -52,7 +54,7 @@ class BooleanEvaluationResponse(BaseModel):
     timestamp: str
 
 
-class ErrorEvaluationReponse(BaseModel):
+class ErrorEvaluationResponse(BaseModel):
     flag_key: str = Field(..., alias="flagKey")
     namespace_key: str = Field(..., alias="namespaceKey")
     reason: ErrorEvaluationReason
@@ -66,7 +68,7 @@ class EvaluationResponse(BaseModel):
     variant_response: Optional[VariantEvaluationResponse] = Field(
         default=None, alias="variantResponse"
     )
-    error_response: Optional[ErrorEvaluationReponse] = Field(
+    error_response: Optional[ErrorEvaluationResponse] = Field(
         default=None, alias="errorResponse"
     )
 
diff --git a/flipt-rust/src/evaluation/models.rs b/flipt-rust/src/evaluation/models.rs
index cd82c7f..de9d536 100644
--- a/flipt-rust/src/evaluation/models.rs
+++ b/flipt-rust/src/evaluation/models.rs
@@ -5,6 +5,7 @@ use std::collections::HashMap;
 #[derive(Default, Serialize)]
 pub struct BatchEvaluationRequest {
     pub requests: Vec<EvaluationRequest>,
+    pub reference: Option<String>,
 }
 
 #[derive(Serialize)]
@@ -14,6 +15,7 @@ pub struct EvaluationRequest {
     pub flag_key: String,
     pub entity_id: String,
     pub context: HashMap<String, String>,
+    pub reference: Option<String>,
 }
 
 #[derive(Debug, Clone, PartialEq, Deserialize)]
diff --git a/flipt-rust/tests/integration.rs b/flipt-rust/tests/integration.rs
index b764601..2be4c02 100644
--- a/flipt-rust/tests/integration.rs
+++ b/flipt-rust/tests/integration.rs
@@ -27,12 +27,14 @@ async fn tests() {
         flag_key: "flag1".into(),
         entity_id: "entity".into(),
         context: context.clone(),
+        reference: None,
     };
     let boolean_request = EvaluationRequest {
         namespace_key: "default".into(),
         flag_key: "flag_boolean".into(),
         entity_id: "entity".into(),
         context: context.clone(),
+        reference: None,
     };
 
     let variant = flipt_client
@@ -63,9 +65,13 @@ async fn tests() {
         flag_key: "notfound".into(),
         entity_id: "entity".into(),
         context: context.clone(),
+        reference: None,
     });
 
-    let batch_request = BatchEvaluationRequest { requests };
+    let batch_request = BatchEvaluationRequest {
+        requests,
+        reference: None,
+    };
     let batch = flipt_client.evaluation.batch(&batch_request).await.unwrap();
 
     // Variant