fix(bedrock): Only forward anthropic_beta header to Claude models

Fix issue where anthropic_beta header was being sent to all Bedrock models
via the /v1/messages endpoint, causing "unknown variant: anthropic_beta"
errors on non-Claude models like Qwen and Nova.

Changes:
- Use BedrockLLM.get_bedrock_invoke_provider() for robust model detection
- Only add anthropic_beta to request when provider is "anthropic"
- Add comprehensive tests for Claude and non-Claude models
- Update documentation explaining the filtering behavior

This ensures Claude Code works seamlessly with non-Claude Bedrock models
while preserving full anthropic_beta support for Claude models.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: irfansofyana

litellm/llms/bedrock/messages/invoke_transformations/anthropic_claude3_transformation.py

@@ -128,11 +128,16 @@ def transform_anthropic_messages_request(
         # 3. `model` is not allowed in request body for bedrock invoke
         if "model" in anthropic_messages_request:
             anthropic_messages_request.pop("model", None)
-            
-        # 4. Handle anthropic_beta from user headers
-        anthropic_beta_list = get_anthropic_beta_from_headers(headers)
-        if anthropic_beta_list:
-            anthropic_messages_request["anthropic_beta"] = anthropic_beta_list
+
+        # 4. Handle anthropic_beta from user headers - ONLY for Claude models
+        # Use robust provider detection to avoid sending unsupported headers to non-Claude models
+        from litellm import BedrockLLM
+
+        bedrock_provider = BedrockLLM.get_bedrock_invoke_provider(model=model)
+        if bedrock_provider == "anthropic":
+            anthropic_beta_list = get_anthropic_beta_from_headers(headers)
+            if anthropic_beta_list:
+                anthropic_messages_request["anthropic_beta"] = anthropic_beta_list
 
         return anthropic_messages_request
 

litellm/llms/bedrock/messages/readme.md

@@ -1,3 +1,10 @@
 # /v1/messages
 
-This folder contains transformation logic for calling bedrock models in the Anthropic /v1/messages API spec.
+This folder contains transformation logic for calling bedrock models in the Anthropic /v1/messages API spec.
+
+## Important Notes
+
+- The `anthropic_beta` header is only forwarded to **Claude models** (models with provider "anthropic")
+- Non-Claude models (Qwen, Nova, etc.) will have this header stripped automatically
+- This prevents "unknown variant: anthropic_beta" errors on models that don't support Anthropic beta features
+- Provider detection is performed using `BedrockLLM.get_bedrock_invoke_provider()` for robust model identification

tests/test_litellm/llms/bedrock/test_anthropic_beta_support.py

@@ -163,4 +163,48 @@ def test_anthropic_beta_all_supported_features(self):
         )
 
         assert "anthropic_beta" in result
-        assert result["anthropic_beta"] == supported_features
+        assert result["anthropic_beta"] == supported_features
+
+    def test_anthropic_beta_excluded_for_non_claude_models(self):
+        """Test that anthropic_beta is NOT included for non-Claude models using provider detection."""
+        config = AmazonAnthropicClaudeMessagesConfig()
+        headers = {"anthropic-beta": "some-beta-feature"}
+
+        # Test with Qwen model (various formats)
+        for qwen_model in ["qwen3-72b", "bedrock/qwen3-72b", "qwen.qwen3-72b-v1:0"]:
+            result = config.transform_anthropic_messages_request(
+                model=qwen_model,
+                messages=[{"role": "user", "content": "test"}],
+                anthropic_messages_optional_request_params={},
+                litellm_params={},
+                headers=headers,
+            )
+            # anthropic_beta should NOT be in the request for non-Claude models
+            assert "anthropic_beta" not in result, f"anthropic_beta should not be present for {qwen_model}"
+
+        # Test with Nova model
+        result_nova = config.transform_anthropic_messages_request(
+            model="us.amazon.nova-pro-v1:0",
+            messages=[{"role": "user", "content": "test"}],
+            anthropic_messages_optional_request_params={},
+            litellm_params={},
+            headers=headers,
+        )
+        assert "anthropic_beta" not in result_nova
+
+        # Test with Claude models (various formats)
+        for claude_model in [
+            "anthropic.claude-3-5-sonnet-20240620-v1:0",
+            "invoke/anthropic.claude-3-5-sonnet-20240620-v1:0",
+            "bedrock/claude-3-5-sonnet",
+        ]:
+            result_claude = config.transform_anthropic_messages_request(
+                model=claude_model,
+                messages=[{"role": "user", "content": "test"}],
+                anthropic_messages_optional_request_params={},
+                litellm_params={},
+                headers=headers,
+            )
+            # anthropic_beta SHOULD be in the request for Claude models
+            assert "anthropic_beta" in result_claude, f"anthropic_beta should be present for {claude_model}"
+            assert result_claude["anthropic_beta"] == ["some-beta-feature"]