From c13dcb0abfe3de7b6722e18d7acf0f59eaa39fc8 Mon Sep 17 00:00:00 2001
From: mateo-berri <277851410+mateo-berri@users.noreply.github.com>
Date: Sat, 19 Sep 2026 20:11:14 -0700
Subject: [PATCH] fix(proxy): forward a client's anthropic-beta and
 anthropic-version headers to bedrock_mantle

---
 litellm/proxy/litellm_pre_call_utils.py       |  7 +++++-
 ..._bedrock_mantle_messages_transformation.py | 19 +++++++++++++++
 .../proxy/test_litellm_pre_call_utils.py      | 24 ++++++++++++++++++-
 3 files changed, 48 insertions(+), 2 deletions(-)

diff --git a/litellm/proxy/litellm_pre_call_utils.py b/litellm/proxy/litellm_pre_call_utils.py
index 9a973755894..e415a78f412 100644
--- a/litellm/proxy/litellm_pre_call_utils.py
+++ b/litellm/proxy/litellm_pre_call_utils.py
@@ -3418,7 +3418,12 @@ async def add_guardrails_from_policy_engine(
 
 
 _ANTHROPIC_API_HEADER_PROVIDERS: Final = ",".join(
-    (LlmProviders.ANTHROPIC.value, LlmProviders.BEDROCK.value, LlmProviders.VERTEX_AI.value)
+    (
+        LlmProviders.ANTHROPIC.value,
+        LlmProviders.BEDROCK.value,
+        LlmProviders.BEDROCK_MANTLE.value,
+        LlmProviders.VERTEX_AI.value,
+    )
 )
 _ANTHROPIC_OAUTH_CREDENTIAL_PROVIDERS: Final = LlmProviders.ANTHROPIC.value
 
diff --git a/tests/test_litellm/llms/bedrock_mantle/test_bedrock_mantle_messages_transformation.py b/tests/test_litellm/llms/bedrock_mantle/test_bedrock_mantle_messages_transformation.py
index 3544262996c..6bacf8f3d94 100644
--- a/tests/test_litellm/llms/bedrock_mantle/test_bedrock_mantle_messages_transformation.py
+++ b/tests/test_litellm/llms/bedrock_mantle/test_bedrock_mantle_messages_transformation.py
@@ -385,6 +385,25 @@ class TestBetaHeadersOnTheWire:
             "interleaved-thinking-2025-05-14",
         ]
 
+    @pytest.mark.asyncio
+    @respx.mock
+    async def test_betas_a_proxy_client_sends_reach_mantle_filtered(self):
+        from litellm.proxy.litellm_pre_call_utils import add_provider_specific_headers_to_request
+
+        proxy_request_data: dict = {}
+        add_provider_specific_headers_to_request(
+            data=proxy_request_data,
+            headers={
+                "anthropic-beta": "claude-code-20250219,fast-mode-2026-02-01,interleaved-thinking-2025-05-14",
+                "anthropic-version": "2023-06-01",
+                "user-agent": "claude-cli/2.1.239",
+            },
+        )
+
+        route = await self._send(**proxy_request_data)
+
+        assert _sent_betas(route) == ["claude-code-20250219", "interleaved-thinking-2025-05-14"]
+
     @pytest.mark.asyncio
     @respx.mock
     async def test_betas_mantle_rejects_are_dropped_before_the_request(self):
diff --git a/tests/test_litellm/proxy/test_litellm_pre_call_utils.py b/tests/test_litellm/proxy/test_litellm_pre_call_utils.py
index 88d38d74f49..9257a2dd23d 100644
--- a/tests/test_litellm/proxy/test_litellm_pre_call_utils.py
+++ b/tests/test_litellm/proxy/test_litellm_pre_call_utils.py
@@ -7249,7 +7249,7 @@ CROSS_ACCOUNT_AUTHORIZATION = "Bearer deliberately-configured-pass-through-token
 
 SIGV4_PREFIX = "AWS4-HMAC-SHA256"
 AUTHORIZATION_HEADER_CASINGS = ["authorization", "Authorization", "AUTHORIZATION"]
-LEAK_TARGET_PROVIDERS = ["bedrock", "bedrock_converse", "vertex_ai"]
+LEAK_TARGET_PROVIDERS = ["bedrock", "bedrock_converse", "bedrock_mantle", "vertex_ai"]
 
 BEDROCK_ENDPOINT = (
     "https://bedrock-runtime.us-west-2.amazonaws.com/model/us.anthropic.claude-sonnet-4-5-20250929-v1:0/invoke"
@@ -7342,6 +7342,28 @@ def test_oauth_credential_entry_is_scoped_to_anthropic_alone():
     assert [entry["custom_llm_provider"] for entry in credential_entries] == ["anthropic"]
 
 
+@pytest.mark.parametrize("custom_llm_provider", ["anthropic", "bedrock", "bedrock_mantle", "vertex_ai"])
+def test_client_anthropic_api_headers_reach_every_anthropic_messages_provider(custom_llm_provider):
+    client_headers = {
+        "anthropic-beta": "claude-code-20250219,interleaved-thinking-2025-05-14",
+        "anthropic-version": "2023-06-01",
+        "user-agent": "claude-cli/2.1.239",
+    }
+
+    forwarded = _headers_forwarded_to(client_headers, custom_llm_provider)
+
+    assert forwarded == {
+        "anthropic-beta": "claude-code-20250219,interleaved-thinking-2025-05-14",
+        "anthropic-version": "2023-06-01",
+    }
+
+
+def test_client_anthropic_api_headers_stay_off_openai_compatible_providers():
+    forwarded = _headers_forwarded_to({"anthropic-beta": "claude-code-20250219"}, "openai")
+
+    assert forwarded == {}
+
+
 def test_no_provider_specific_header_when_client_sends_nothing_anthropic():
     data: dict = {}
     add_provider_specific_headers_to_request(