diff --git a/README.md b/README.md
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@@ -1,5 +1,10 @@
 # Ray TPU
 
+> [!NOTE]
+> This project is no longer under active development. Most of its capabilities,
+> including multi-host/multi-slice, have been [upstreamed](https://github.com/ray-project/ray/blob/master/python/ray/util/tpu.py)
+> to OSS Ray.
+
 This is a repository containing utilities for running [Ray](https://www.ray.io/)
 on Cloud TPUs. For more information about TPUs, please check out the official
 Google Cloud documentation [here](https://cloud.google.com/tpu).