fix(bedrock): send the anthropic-workspace-id header to Bedrock Mantle (#44173)

aws_bedrock_project_id reached Bedrock Mantle as anthropic-workspace, a
header AWS ignores, so requests ran under account defaults and models
that require a project data-retention mode failed with a 400. Send the
header AWS documents, anthropic-workspace-id, on both Mantle routes.

Re-lands #31994 by @gunjanjaswal, merged into the since-deleted
litellm_oss_staging branch on 2026-08-22, which never reached main.

Fixes #31947

Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>

litellm/llms/bedrock/chat/mantle/transformation.py

@@ -73,7 +73,7 @@ class AmazonMantleConfig(AmazonAnthropicClaudeConfig):
         )
         project_id: Final = litellm_params.get("aws_bedrock_project_id")
         if project_id:
-            headers["anthropic-workspace"] = project_id
+            headers["anthropic-workspace-id"] = project_id
         return headers
 
     def transform_request(

litellm/llms/bedrock/messages/mantle_transformation.py

@@ -104,7 +104,7 @@ class AmazonMantleMessagesConfig(AmazonAnthropicClaudeMessagesConfig):
             {
                 name: value
                 for name, value in (
-                    ("anthropic-workspace", project_id),
+                    ("anthropic-workspace-id", project_id),
                     ("anthropic-version", None if has_version else DEFAULT_ANTHROPIC_API_VERSION),
                 )
                 if value

tests/unit/llms/bedrock/test_mantle.py

@@ -18,6 +18,10 @@ from litellm.llms.bedrock.messages.mantle_transformation import (
     AmazonMantleMessagesConfig,
 )
 
+# AWS names this header for Mantle workspaces on the Anthropic Messages API, checked 2026-10-02:
+# https://docs.aws.amazon.com/bedrock/latest/userguide/workspaces.html
+_MANTLE_WORKSPACE_HEADER = "anthropic-workspace-id"
+
 
 def _anthropic_response(url: str) -> httpx.Response:
     return httpx.Response(
@@ -345,7 +349,7 @@ def test_mantle_validate_environment_sets_workspace_header():
         optional_params={},
         litellm_params={"aws_bedrock_project_id": "proj_abc123def456"},
     )
-    assert headers["anthropic-workspace"] == "proj_abc123def456"
+    assert headers[_MANTLE_WORKSPACE_HEADER] == "proj_abc123def456"
 
 
 def test_mantle_validate_environment_without_project_id():
@@ -357,7 +361,7 @@ def test_mantle_validate_environment_without_project_id():
         optional_params={},
         litellm_params={"aws_bedrock_project_id": None},
     )
-    assert "anthropic-workspace" not in headers
+    assert _MANTLE_WORKSPACE_HEADER not in headers
 
 
 def test_mantle_messages_validate_environment_sets_workspace_header():
@@ -370,7 +374,7 @@ def test_mantle_messages_validate_environment_sets_workspace_header():
         litellm_params={"aws_bedrock_project_id": "proj_abc123def456"},
         api_base="https://bedrock-mantle.us-east-1.api.aws/anthropic/v1/messages",
     )
-    assert headers["anthropic-workspace"] == "proj_abc123def456"
+    assert headers[_MANTLE_WORKSPACE_HEADER] == "proj_abc123def456"
     assert api_base == "https://bedrock-mantle.us-east-1.api.aws/anthropic/v1/messages"
 
 
@@ -383,7 +387,7 @@ def test_mantle_messages_validate_environment_without_project_id():
         optional_params={},
         litellm_params={},
     )
-    assert "anthropic-workspace" not in headers
+    assert _MANTLE_WORKSPACE_HEADER not in headers
 
 
 def test_mantle_completion_sends_workspace_header_and_clean_body():
@@ -409,7 +413,7 @@ def test_mantle_completion_sends_workspace_header_and_clean_body():
     assert response.choices[0].message.content == "ok"
     assert len(requests) == 1
     assert requests[0]["path"] == "/anthropic/v1/messages"
-    assert requests[0]["headers"]["anthropic-workspace"] == "proj_abc123def456"
+    assert requests[0]["headers"][_MANTLE_WORKSPACE_HEADER] == "proj_abc123def456"
     assert "aws_bedrock_project_id" not in requests[0]["body"]
 
 
@@ -443,7 +447,7 @@ async def test_mantle_anthropic_messages_sends_workspace_header_and_clean_body()
     assert response["content"][0]["text"] == "ok"
     assert len(requests) == 1
     assert requests[0]["path"] == "/anthropic/v1/messages"
-    assert requests[0]["headers"]["anthropic-workspace"] == "proj_abc123def456"
+    assert requests[0]["headers"][_MANTLE_WORKSPACE_HEADER] == "proj_abc123def456"
     assert "aws_bedrock_project_id" not in requests[0]["body"]
 
 

tests/unit/llms/bedrock_mantle/test_bedrock_mantle_messages_transformation.py

@@ -193,7 +193,8 @@ class TestEnvironment:
         assert "anthropic-version" not in merged
 
     def test_project_id_becomes_the_workspace_header(self):
-        assert self._validate({}, {"aws_bedrock_project_id": "proj_123"})["anthropic-workspace"] == "proj_123"
+        # header name from https://docs.aws.amazon.com/bedrock/latest/userguide/workspaces.html, checked 2026-10-02
+        assert self._validate({}, {"aws_bedrock_project_id": "proj_123"})["anthropic-workspace-id"] == "proj_123"
 
 
 class TestRequestBody: