diff --git a/letta/server/rest_api/routers/v1/anthropic.py b/letta/server/rest_api/routers/v1/anthropic.py
index b3399451..a25d12c0 100644
--- a/letta/server/rest_api/routers/v1/anthropic.py
+++ b/letta/server/rest_api/routers/v1/anthropic.py
@@ -323,7 +323,8 @@ async def anthropic_messages_proxy(
         request_data = json.loads(body)
         is_streaming = request_data.get("stream", False)
         model_name = request_data.get("model")
-        project_id = request_data.get("project_id")
+        # Extract and remove project_id (internal use only, not for Anthropic API)
+        project_id = request_data.pop("project_id", None)
         logger.debug(f"[Anthropic Proxy] Request is streaming: {is_streaming}")
         logger.debug(f"[Anthropic Proxy] Model: {model_name}")
         logger.debug(f"[Anthropic Proxy] Project ID: {project_id}")