Add v1/messages support for azure anthropic models

docs/my-website/docs/providers/azure/azure_anthropic.md

@@ -19,7 +19,7 @@ Azure Foundry supports the following Claude models:
 | Provider Route on LiteLLM | `azure/` (add this prefix to Claude model names - e.g. `azure/claude-sonnet-4-5`) |
 | Provider Doc | [Azure Foundry Claude Models ↗](https://learn.microsoft.com/en-us/azure/ai-services/foundry-models/claude) |
 | API Endpoint | `https://<resource-name>.services.ai.azure.com/anthropic/v1/messages` |
-| Supported Endpoints | `/chat/completions`, `/anthropic/v1/messages` (passthrough) |
+| Supported Endpoints | `/chat/completions`, `/anthropic/v1/messages`|
 
 ## Key Features
 

litellm/llms/azure/anthropic/__init__.py

@@ -4,5 +4,9 @@ Azure Anthropic provider - supports Claude models via Azure Foundry
 from .handler import AzureAnthropicChatCompletion
 from .transformation import AzureAnthropicConfig
 
-__all__ = ["AzureAnthropicChatCompletion", "AzureAnthropicConfig"]
+try:
+    from .messages_transformation import AzureAnthropicMessagesConfig
+    __all__ = ["AzureAnthropicChatCompletion", "AzureAnthropicConfig", "AzureAnthropicMessagesConfig"]
+except ImportError:
+    __all__ = ["AzureAnthropicChatCompletion", "AzureAnthropicConfig"]
 

litellm/llms/azure/anthropic/messages_transformation.py

@@ -0,0 +1,125 @@
+"""
+Azure Anthropic messages transformation config - extends AnthropicMessagesConfig with Azure authentication
+"""
+from typing import TYPE_CHECKING, Any, Dict, List, Optional, Tuple
+
+import httpx
+
+from litellm.litellm_core_utils.litellm_logging import Logging as LiteLLMLoggingObj, verbose_logger
+from litellm.llms.anthropic.experimental_pass_through.messages.transformation import (
+    AnthropicMessagesConfig,
+)
+from litellm.llms.azure.common_utils import BaseAzureLLM
+from litellm.types.llms.anthropic_messages.anthropic_response import (
+    AnthropicMessagesResponse,
+)
+from litellm.types.router import GenericLiteLLMParams
+
+if TYPE_CHECKING:
+    pass
+
+
+class AzureAnthropicMessagesConfig(AnthropicMessagesConfig):
+    """
+    Azure Anthropic messages configuration that extends AnthropicMessagesConfig.
+    The only difference is authentication - Azure uses x-api-key header (not api-key)
+    and Azure endpoint format.
+    """
+
+    def validate_anthropic_messages_environment(
+        self,
+        headers: dict,
+        model: str,
+        messages: List[Any],
+        optional_params: dict,
+        litellm_params: dict,
+        api_key: Optional[str] = None,
+        api_base: Optional[str] = None,
+    ) -> Tuple[dict, Optional[str]]:
+        """
+        Validate environment and set up Azure authentication headers for /v1/messages endpoint.
+        Azure Anthropic uses x-api-key header (not api-key).
+        """
+        from litellm.secret_managers.main import get_secret_str
+
+        # Convert dict to GenericLiteLLMParams if needed
+        if isinstance(litellm_params, dict):
+            if api_key and "api_key" not in litellm_params:
+                litellm_params = {**litellm_params, "api_key": api_key}
+            litellm_params_obj = GenericLiteLLMParams(**litellm_params)
+        else:
+            litellm_params_obj = litellm_params or GenericLiteLLMParams()
+            if api_key and not litellm_params_obj.api_key:
+                litellm_params_obj.api_key = api_key
+
+        # Use Azure authentication logic
+        headers = BaseAzureLLM._base_validate_azure_environment(
+            headers=headers, litellm_params=litellm_params_obj
+        )
+
+        # Azure Anthropic uses x-api-key header (not api-key)
+        # Convert api-key to x-api-key if present
+        if "api-key" in headers and "x-api-key" not in headers:
+            headers["x-api-key"] = headers.pop("api-key")
+
+        # Set anthropic-version header
+        if "anthropic-version" not in headers:
+            headers["anthropic-version"] = "2023-06-01"
+
+        # Set content-type header
+        if "content-type" not in headers:
+            headers["content-type"] = "application/json"
+
+        # Update headers with optional anthropic beta features
+        headers = self._update_headers_with_optional_anthropic_beta(
+            headers=headers,
+            context_management=optional_params.get("context_management"),
+        )
+
+        return headers, api_base
+
+    def get_complete_url(
+        self,
+        api_base: Optional[str],
+        api_key: Optional[str],
+        model: str,
+        optional_params: dict,
+        litellm_params: dict,
+        stream: Optional[bool] = None,
+    ) -> str:
+        """
+        Get the complete URL for Azure Anthropic /v1/messages endpoint.
+        Azure Foundry endpoint format: https://<resource-name>.services.ai.azure.com/anthropic/v1/messages
+        """
+        from litellm.secret_managers.main import get_secret_str
+
+        api_base = api_base or get_secret_str("AZURE_API_BASE")
+        if api_base is None:
+            raise ValueError(
+                "Missing Azure API Base - Please set `api_base` or `AZURE_API_BASE` environment variable. "
+                "Expected format: https://<resource-name>.services.ai.azure.com/anthropic"
+            )
+
+        # Ensure the URL ends with /v1/messages
+        api_base = api_base.rstrip("/")
+        if api_base.endswith("/v1/messages"):
+            # Already correct
+            pass
+        elif api_base.endswith("/anthropic/v1/messages"):
+            # Already correct
+            pass
+        else:
+            # Check if /anthropic is already in the path
+            if "/anthropic" in api_base:
+                # /anthropic exists, ensure we end with /anthropic/v1/messages
+                # Extract the base URL up to and including /anthropic
+                parts = api_base.split("/anthropic", 1)
+                api_base = parts[0] + "/anthropic"
+            else:
+                # /anthropic not in path, add it
+                api_base = api_base + "/anthropic"
+            # Add /v1/messages
+            api_base = api_base + "/v1/messages"
+
+        return api_base
+

litellm/utils.py

@@ -7341,6 +7341,12 @@ class ProviderConfigManager:
                 )
 
                 return VertexAIPartnerModelsAnthropicMessagesConfig()
+        elif litellm.LlmProviders.AZURE_ANTHROPIC == provider:
+            from litellm.llms.azure.anthropic.messages_transformation import (
+                AzureAnthropicMessagesConfig,
+            )
+
+            return AzureAnthropicMessagesConfig()
         return None
 
     @staticmethod