feat(bedrock_mantle): route Responses API to native OpenAI endpoint

Register BedrockMantleResponsesAPIConfig so /v1/responses hits
bedrock-mantle.{region}.api.aws/openai/v1/responses instead of the
chat-completions fallback. Fix default api_base to use /openai/v1.

Co-authored-by: Cursor <cursoragent@cursor.com>

litellm/__init__.py

@@ -1680,6 +1680,9 @@ if TYPE_CHECKING:
     from .llms.bedrock_mantle.chat.transformation import (
         BedrockMantleChatConfig as BedrockMantleChatConfig,
     )
+    from .llms.bedrock_mantle.responses.transformation import (
+        BedrockMantleResponsesAPIConfig as BedrockMantleResponsesAPIConfig,
+    )
     from .llms.a2a.chat.transformation import A2AConfig as A2AConfig
     from .llms.voyage.embedding.transformation import (
         VoyageEmbeddingConfig as VoyageEmbeddingConfig,

litellm/_lazy_imports_registry.py

@@ -219,6 +219,7 @@ LLM_CONFIG_NAMES = (
     "OpenAITextCompletionConfig",
     "GroqChatConfig",
     "BedrockMantleChatConfig",
+    "BedrockMantleResponsesAPIConfig",
     "A2AConfig",
     "GenAIHubOrchestrationConfig",
     "VoyageEmbeddingConfig",
@@ -886,6 +887,10 @@ _LLM_CONFIGS_IMPORT_MAP = {
         ".llms.bedrock_mantle.chat.transformation",
         "BedrockMantleChatConfig",
     ),
+    "BedrockMantleResponsesAPIConfig": (
+        ".llms.bedrock_mantle.responses.transformation",
+        "BedrockMantleResponsesAPIConfig",
+    ),
     "A2AConfig": (".llms.a2a.chat.transformation", "A2AConfig"),
     "GenAIHubOrchestrationConfig": (
         ".llms.sap.chat.transformation",

litellm/llms/bedrock_mantle/chat/transformation.py

@@ -3,7 +3,7 @@ Amazon Bedrock Mantle - OpenAI-compatible inference engine in Amazon Bedrock.
 
 API docs: https://docs.aws.amazon.com/bedrock/latest/userguide/bedrock-mantle.html
 
-Base URL: https://bedrock-mantle.{region}.api.aws/v1
+Base URL: https://bedrock-mantle.{region}.api.aws/openai/v1
 Auth: AWS Bedrock API key as Bearer token (set via BEDROCK_MANTLE_API_KEY env var)
       or region-aware key via BEDROCK_MANTLE_{REGION}_API_KEY.
 """
@@ -43,7 +43,7 @@ class BedrockMantleChatConfig(OpenAILikeChatConfig):
         api_base = (
             api_base
             or get_secret_str("BEDROCK_MANTLE_API_BASE")
-            or f"https://bedrock-mantle.{region}.api.aws/v1"
+            or f"https://bedrock-mantle.{region}.api.aws/openai/v1"
         )
         dynamic_api_key = api_key or get_secret_str("BEDROCK_MANTLE_API_KEY")
         return api_base, dynamic_api_key

litellm/llms/bedrock_mantle/responses/transformation.py

@@ -0,0 +1,61 @@
+"""
+Amazon Bedrock Mantle - OpenAI-compatible Responses API.
+
+Routes /v1/responses to the provider's native Responses endpoint instead of
+the chat-completions translation fallback.
+"""
+
+from typing import Optional
+
+from litellm.llms.bedrock_mantle.chat.transformation import BedrockMantleChatConfig
+from litellm.llms.openai.responses.transformation import OpenAIResponsesAPIConfig
+from litellm.types.router import GenericLiteLLMParams
+from litellm.types.utils import LlmProviders
+
+
+class BedrockMantleResponsesAPIConfig(OpenAIResponsesAPIConfig):
+    @property
+    def custom_llm_provider(self) -> LlmProviders:
+        return LlmProviders.BEDROCK_MANTLE
+
+    def validate_environment(
+        self,
+        headers: dict,
+        model: str,
+        litellm_params: Optional[GenericLiteLLMParams],
+    ) -> dict:
+        litellm_params = litellm_params or GenericLiteLLMParams()
+        _, api_key = BedrockMantleChatConfig()._get_openai_compatible_provider_info(
+            api_base=litellm_params.api_base,
+            api_key=litellm_params.api_key,
+        )
+        if api_key:
+            headers["Authorization"] = f"Bearer {api_key}"
+        return headers
+
+    def get_complete_url(
+        self,
+        api_base: Optional[str],
+        litellm_params: dict,
+    ) -> str:
+        (
+            resolved_api_base,
+            _,
+        ) = BedrockMantleChatConfig()._get_openai_compatible_provider_info(
+            api_base=api_base or litellm_params.get("api_base"),
+            api_key=litellm_params.get("api_key"),
+        )
+        if not resolved_api_base:
+            raise ValueError(
+                "api_base is required for bedrock_mantle Responses API. "
+                "Set BEDROCK_MANTLE_API_BASE or BEDROCK_MANTLE_REGION."
+            )
+        api_base = resolved_api_base.rstrip("/")
+        if api_base.endswith("/responses"):
+            return api_base
+        if api_base.endswith("/v1"):
+            return f"{api_base}/responses"
+        return f"{api_base}/v1/responses"
+
+    def supports_native_websocket(self) -> bool:
+        return False

litellm/utils.py

@@ -8865,6 +8865,8 @@ class ProviderConfigManager:
             return litellm.OpenRouterResponsesAPIConfig()
         elif litellm.LlmProviders.HOSTED_VLLM == provider:
             return litellm.HostedVLLMResponsesAPIConfig()
+        elif litellm.LlmProviders.BEDROCK_MANTLE == provider:
+            return litellm.BedrockMantleResponsesAPIConfig()
         return None
 
     @staticmethod

tests/test_litellm/llms/bedrock_mantle/test_bedrock_mantle_transformation.py

@@ -14,7 +14,11 @@ import pytest
 
 import litellm
 from litellm.llms.bedrock_mantle.chat.transformation import BedrockMantleChatConfig
+from litellm.llms.bedrock_mantle.responses.transformation import (
+    BedrockMantleResponsesAPIConfig,
+)
 from litellm.types.utils import LlmProviders
+from litellm.utils import ProviderConfigManager
 
 
 class TestBedrockMantleProviderRegistration:
@@ -50,7 +54,7 @@ class TestBedrockMantleConfig:
         monkeypatch.delenv("BEDROCK_MANTLE_API_BASE", raising=False)
         cfg = BedrockMantleChatConfig()
         api_base, _ = cfg._get_openai_compatible_provider_info(None, None)
-        assert api_base == "https://bedrock-mantle.eu-west-1.api.aws/v1"
+        assert api_base == "https://bedrock-mantle.eu-west-1.api.aws/openai/v1"
 
     def test_default_api_base_uses_aws_region(self, monkeypatch):
         monkeypatch.delenv("BEDROCK_MANTLE_REGION", raising=False)
@@ -58,7 +62,7 @@ class TestBedrockMantleConfig:
         monkeypatch.setenv("AWS_REGION", "ap-northeast-1")
         cfg = BedrockMantleChatConfig()
         api_base, _ = cfg._get_openai_compatible_provider_info(None, None)
-        assert api_base == "https://bedrock-mantle.ap-northeast-1.api.aws/v1"
+        assert api_base == "https://bedrock-mantle.ap-northeast-1.api.aws/openai/v1"
 
     def test_default_api_base_fallback_to_us_east_1(self, monkeypatch):
         monkeypatch.delenv("BEDROCK_MANTLE_REGION", raising=False)
@@ -66,10 +70,10 @@ class TestBedrockMantleConfig:
         monkeypatch.delenv("AWS_REGION", raising=False)
         cfg = BedrockMantleChatConfig()
         api_base, _ = cfg._get_openai_compatible_provider_info(None, None)
-        assert api_base == "https://bedrock-mantle.us-east-1.api.aws/v1"
+        assert api_base == "https://bedrock-mantle.us-east-1.api.aws/openai/v1"
 
     def test_custom_api_base_overrides_default(self, monkeypatch):
-        custom_base = "https://bedrock-mantle.us-west-2.api.aws/v1"
+        custom_base = "https://bedrock-mantle.us-west-2.api.aws/openai/v1"
         cfg = BedrockMantleChatConfig()
         api_base, _ = cfg._get_openai_compatible_provider_info(custom_base, None)
         assert api_base == custom_base
@@ -96,6 +100,21 @@ class TestBedrockMantleConfig:
         assert "max_tokens" in params
 
 
+class TestBedrockMantleResponsesConfig:
+    def test_responses_complete_url(self, monkeypatch):
+        monkeypatch.setenv("BEDROCK_MANTLE_REGION", "us-east-1")
+        cfg = BedrockMantleResponsesAPIConfig()
+        url = cfg.get_complete_url(api_base=None, litellm_params={})
+        assert url == "https://bedrock-mantle.us-east-1.api.aws/openai/v1/responses"
+
+    def test_provider_config_manager_registers_responses(self):
+        cfg = ProviderConfigManager.get_provider_responses_api_config(
+            provider="bedrock_mantle",
+            model="gpt-5.5",
+        )
+        assert isinstance(cfg, BedrockMantleResponsesAPIConfig)
+
+
 class TestBedrockMantleProviderResolution:
     def test_get_llm_provider_resolves_correctly(self):
         model, provider, _, _ = litellm.get_llm_provider(