diff --git a/.release-please-manifest.json b/.release-please-manifest.json
index 6b46767..0056f0a 100644
--- a/.release-please-manifest.json
+++ b/.release-please-manifest.json
@@ -1,3 +1,3 @@
 {
-  ".": "4.9.0"
+  ".": "4.9.1"
 }
\ No newline at end of file
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5618fa3..d183d7d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,13 @@
 # Changelog
 
+## 4.9.1 (2026-02-07)
+
+Full Changelog: [v4.9.0...v4.9.1](https://github.com/trycourier/courier-java/compare/v4.9.0...v4.9.1)
+
+### Chores
+
+* **internal:** upgrade AssertJ ([afe545e](https://github.com/trycourier/courier-java/commit/afe545eaebadf882a5bea38b08d2a31fc8c8289b))
+
 ## 4.9.0 (2026-02-06)
 
 Full Changelog: [v4.8.0...v4.9.0](https://github.com/trycourier/courier-java/compare/v4.8.0...v4.9.0)
diff --git a/README.md b/README.md
index 689f7a5..cfa93e1 100644
--- a/README.md
+++ b/README.md
@@ -2,8 +2,8 @@
 
 <!-- x-release-please-start-version -->
 
-[![Maven Central](https://img.shields.io/maven-central/v/com.courier/courier-java)](https://central.sonatype.com/artifact/com.courier/courier-java/4.9.0)
-[![javadoc](https://javadoc.io/badge2/com.courier/courier-java/4.9.0/javadoc.svg)](https://javadoc.io/doc/com.courier/courier-java/4.9.0)
+[![Maven Central](https://img.shields.io/maven-central/v/com.courier/courier-java)](https://central.sonatype.com/artifact/com.courier/courier-java/4.9.1)
+[![javadoc](https://javadoc.io/badge2/com.courier/courier-java/4.9.1/javadoc.svg)](https://javadoc.io/doc/com.courier/courier-java/4.9.1)
 
 <!-- x-release-please-end -->
 
@@ -13,7 +13,7 @@ It is generated with [Stainless](https://www.stainless.com/).
 
 <!-- x-release-please-start-version -->
 
-The REST API documentation can be found on [www.courier.com](https://www.courier.com/docs). Javadocs are available on [javadoc.io](https://javadoc.io/doc/com.courier/courier-java/4.9.0).
+The REST API documentation can be found on [www.courier.com](https://www.courier.com/docs). Javadocs are available on [javadoc.io](https://javadoc.io/doc/com.courier/courier-java/4.9.1).
 
 <!-- x-release-please-end -->
 
@@ -24,7 +24,7 @@ The REST API documentation can be found on [www.courier.com](https://www.courier
 ### Gradle
 
 ```kotlin
-implementation("com.courier:courier-java:4.9.0")
+implementation("com.courier:courier-java:4.9.1")
 ```
 
 ### Maven
@@ -33,7 +33,7 @@ implementation("com.courier:courier-java:4.9.0")
 <dependency>
   <groupId>com.courier</groupId>
   <artifactId>courier-java</artifactId>
-  <version>4.9.0</version>
+  <version>4.9.1</version>
 </dependency>
 ```
 
diff --git a/build.gradle.kts b/build.gradle.kts
index ca06182..aae0be0 100644
--- a/build.gradle.kts
+++ b/build.gradle.kts
@@ -8,7 +8,7 @@ repositories {
 
 allprojects {
     group = "com.courier"
-    version = "4.9.0" // x-release-please-version
+    version = "4.9.1" // x-release-please-version
 }
 
 subprojects {
diff --git a/courier-java-client-okhttp/build.gradle.kts b/courier-java-client-okhttp/build.gradle.kts
index b8a6c9c..8bb8f61 100644
--- a/courier-java-client-okhttp/build.gradle.kts
+++ b/courier-java-client-okhttp/build.gradle.kts
@@ -10,6 +10,6 @@ dependencies {
     implementation("com.squareup.okhttp3:logging-interceptor:4.12.0")
 
     testImplementation(kotlin("test"))
-    testImplementation("org.assertj:assertj-core:3.25.3")
+    testImplementation("org.assertj:assertj-core:3.27.7")
     testImplementation("com.github.tomakehurst:wiremock-jre8:2.35.2")
 }
diff --git a/courier-java-core/build.gradle.kts b/courier-java-core/build.gradle.kts
index 3396f58..15e9f37 100644
--- a/courier-java-core/build.gradle.kts
+++ b/courier-java-core/build.gradle.kts
@@ -33,7 +33,7 @@ dependencies {
     testImplementation(kotlin("test"))
     testImplementation(project(":courier-java-client-okhttp"))
     testImplementation("com.github.tomakehurst:wiremock-jre8:2.35.2")
-    testImplementation("org.assertj:assertj-core:3.25.3")
+    testImplementation("org.assertj:assertj-core:3.27.7")
     testImplementation("org.junit.jupiter:junit-jupiter-api:5.9.3")
     testImplementation("org.junit.jupiter:junit-jupiter-params:5.9.3")
     testImplementation("org.junit-pioneer:junit-pioneer:1.9.1")
diff --git a/courier-java-proguard-test/build.gradle.kts b/courier-java-proguard-test/build.gradle.kts
index 0d3c8c1..5a61034 100644
--- a/courier-java-proguard-test/build.gradle.kts
+++ b/courier-java-proguard-test/build.gradle.kts
@@ -18,7 +18,7 @@ dependencies {
     testImplementation(project(":courier-java"))
     testImplementation(kotlin("test"))
     testImplementation("org.junit.jupiter:junit-jupiter-api:5.9.3")
-    testImplementation("org.assertj:assertj-core:3.25.3")
+    testImplementation("org.assertj:assertj-core:3.27.7")
     testImplementation("com.fasterxml.jackson.module:jackson-module-kotlin:2.14.0")
 }