diff --git a/src/OpenTelemetry.Api.ProviderBuilderExtensions/CHANGELOG.md b/src/OpenTelemetry.Api.ProviderBuilderExtensions/CHANGELOG.md
index 50d43f6ddf4..1f2a27b7f38 100644
--- a/src/OpenTelemetry.Api.ProviderBuilderExtensions/CHANGELOG.md
+++ b/src/OpenTelemetry.Api.ProviderBuilderExtensions/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 ## Unreleased
 
+## 1.9.0-alpha.1
+
+Released 2024-May-20
+
 ## 1.8.1
 
 Released 2024-Apr-17
diff --git a/src/OpenTelemetry.Api/CHANGELOG.md b/src/OpenTelemetry.Api/CHANGELOG.md
index 877dab6b9d1..9bdc9bf5d16 100644
--- a/src/OpenTelemetry.Api/CHANGELOG.md
+++ b/src/OpenTelemetry.Api/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 ## Unreleased
 
+## 1.9.0-alpha.1
+
+Released 2024-May-20
+
 * **Breaking change:** Fix space character encoding from `+` to `%20`
   for baggage item values when propagating baggage as defined in
   [W3C Baggage propagation format specification](https://www.w3.org/TR/baggage/).
diff --git a/src/OpenTelemetry.Exporter.Console/CHANGELOG.md b/src/OpenTelemetry.Exporter.Console/CHANGELOG.md
index 2c0a56df8a1..6605e9d684f 100644
--- a/src/OpenTelemetry.Exporter.Console/CHANGELOG.md
+++ b/src/OpenTelemetry.Exporter.Console/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 ## Unreleased
 
+## 1.9.0-alpha.1
+
+Released 2024-May-20
+
 ## 1.8.1
 
 Released 2024-Apr-17
diff --git a/src/OpenTelemetry.Exporter.InMemory/CHANGELOG.md b/src/OpenTelemetry.Exporter.InMemory/CHANGELOG.md
index a5d6e499957..d4aa853c675 100644
--- a/src/OpenTelemetry.Exporter.InMemory/CHANGELOG.md
+++ b/src/OpenTelemetry.Exporter.InMemory/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 ## Unreleased
 
+## 1.9.0-alpha.1
+
+Released 2024-May-20
+
 ## 1.8.1
 
 Released 2024-Apr-17
diff --git a/src/OpenTelemetry.Exporter.OpenTelemetryProtocol/CHANGELOG.md b/src/OpenTelemetry.Exporter.OpenTelemetryProtocol/CHANGELOG.md
index d8200afd2b1..08310125087 100644
--- a/src/OpenTelemetry.Exporter.OpenTelemetryProtocol/CHANGELOG.md
+++ b/src/OpenTelemetry.Exporter.OpenTelemetryProtocol/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 ## Unreleased
 
+## 1.9.0-alpha.1
+
+Released 2024-May-20
+
 * `User-Agent` header format changed from
   `OTel-OTLP-Exporter-Dotnet/{NuGet Package Version}+{Commit Hash}`
   to `OTel-OTLP-Exporter-Dotnet/{NuGet Package Version}`.
diff --git a/src/OpenTelemetry.Exporter.Zipkin/CHANGELOG.md b/src/OpenTelemetry.Exporter.Zipkin/CHANGELOG.md
index cf72bf0c33f..15dcc2f3396 100644
--- a/src/OpenTelemetry.Exporter.Zipkin/CHANGELOG.md
+++ b/src/OpenTelemetry.Exporter.Zipkin/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 ## Unreleased
 
+## 1.9.0-alpha.1
+
+Released 2024-May-20
+
 ## 1.8.1
 
 Released 2024-Apr-17
diff --git a/src/OpenTelemetry.Extensions.Hosting/CHANGELOG.md b/src/OpenTelemetry.Extensions.Hosting/CHANGELOG.md
index d0f6f22868b..a5921a6dd90 100644
--- a/src/OpenTelemetry.Extensions.Hosting/CHANGELOG.md
+++ b/src/OpenTelemetry.Extensions.Hosting/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 ## Unreleased
 
+## 1.9.0-alpha.1
+
+Released 2024-May-20
+
 * Reverted obsoletion of `OpenTelemetryBuilder`.
   ([#5571](https://github.com/open-telemetry/opentelemetry-dotnet/pull/5571))
 
diff --git a/src/OpenTelemetry.Extensions.Propagators/CHANGELOG.md b/src/OpenTelemetry.Extensions.Propagators/CHANGELOG.md
index 97b2f8c0da5..68d9cd7747f 100644
--- a/src/OpenTelemetry.Extensions.Propagators/CHANGELOG.md
+++ b/src/OpenTelemetry.Extensions.Propagators/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 ## Unreleased
 
+## 1.9.0-alpha.1
+
+Released 2024-May-20
+
 ## 1.8.1
 
 Released 2024-Apr-17
diff --git a/src/OpenTelemetry/CHANGELOG.md b/src/OpenTelemetry/CHANGELOG.md
index ab9ab112b27..763f3f370a0 100644
--- a/src/OpenTelemetry/CHANGELOG.md
+++ b/src/OpenTelemetry/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 ## Unreleased
 
+## 1.9.0-alpha.1
+
+Released 2024-May-20
+
 * **Experimental (pre-release builds only):** Exposed `ExemplarReservoir` as a
   public API and added support for setting an `ExemplarReservoir` factory
   function when configuring a view (applies to individual metrics).