diff --git a/CHANGELOG.md b/CHANGELOG.md
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@@ -0,0 +1,11 @@
+# codex-action Changelog
+
+## [v1.1](https://github.com/openai/codex-action/tree/v1.1) (2005-11-05)
+
+- [#47](https://github.com/openai/codex-action/pull/47) added support for Azure via the new `responses-api-endpoint` parameter
+- [#36](https://github.com/openai/codex-action/pull/36) added `effort` parameter
+- [#45](https://github.com/openai/codex-action/pull/45) pin the commit hash of the `actions/setup-node` action used by `openai/codex-action`
+
+## [v1.0](https://github.com/openai/codex-action/tree/v1.0) (2025-10-06)
+
+- Initial release (OpenAI DevDay 2025!)
diff --git a/README.md b/README.md
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--- a/README.md
+++ b/README.md
@@ -169,6 +169,10 @@ Ultimately, your configured Action might look something like the following:
     prompt: "Debug all the things."
 ```
 
+## Version History
+
+See the [`CHANGELOG`](./CHANGELOG.md) for details.
+
 ## License
 
 This project is licensed under the [Apache License 2.0](./LICENSE).