Merge c54da063f2 into f1795e6d44

litellm-rust/crates/llms-types/src/providers/anthropic/beta.rs

@@ -124,12 +124,14 @@ pub enum AnthropicBeta {
     ToolSearchTool20251019,
     #[strum(serialize = "inline-tools-2026-09-15")]
     InlineTools20260915,
+    #[strum(serialize = "server-side-fallback-2026-07-01")]
+    ServerSideFallback20260701,
     #[strum(default, transparent)]
     Other(String),
 }
 
 impl AnthropicBeta {
-    pub const KNOWN: [Self; 40] = [
+    pub const KNOWN: [Self; 41] = [
         Self::Oauth20250420,
         Self::WebFetch20250910,
         Self::WebSearch20250305,
@@ -170,6 +172,7 @@ impl AnthropicBeta {
         Self::ToolExamples20251029,
         Self::ToolSearchTool20251019,
         Self::InlineTools20260915,
+        Self::ServerSideFallback20260701,
     ];
 
     pub fn as_str(&self) -> &str {
@@ -241,7 +244,7 @@ impl AnthropicBeta {
             | Self::ThinkingBindingControls20260801 => &[],
             Self::DangerousToolUse20260903 => &[BetaProvider::BedrockConverse],
             Self::Effort20251124 => &[BetaProvider::VertexAi],
-            Self::FastMode20260201 | Self::Oauth20250420 => &[
+            Self::FastMode20260201 | Self::Oauth20250420 | Self::ServerSideFallback20260701 => &[
                 BetaProvider::AzureAi,
                 BetaProvider::BedrockConverse,
                 BetaProvider::Bedrock,
@@ -441,7 +444,8 @@ mod tests {
             AnthropicBeta::TokenEfficientTools20250219,
             AnthropicBeta::ToolExamples20251029,
             AnthropicBeta::ToolSearchTool20251019,
-            AnthropicBeta::InlineTools20260915
+            AnthropicBeta::InlineTools20260915,
+            AnthropicBeta::ServerSideFallback20260701
         )]
         beta: AnthropicBeta,
     ) {

litellm/anthropic_beta_headers_config.json

@@ -37,7 +37,8 @@
     "mid-conversation-output-config-2026-07-01": "mid-conversation-output-config-2026-07-01",
     "thinking-display-updates-2026-08-18": "thinking-display-updates-2026-08-18",
     "mid-conversation-tool-changes-2026-07-01": "mid-conversation-tool-changes-2026-07-01",
-    "inline-tools-2026-09-15": "inline-tools-2026-09-15"
+    "inline-tools-2026-09-15": "inline-tools-2026-09-15",
+    "server-side-fallback-2026-07-01": "server-side-fallback-2026-07-01"
   },
   "azure_ai": {
     "advisor-tool-2026-03-01": null,

litellm/llms/anthropic/chat/transformation.py

@@ -105,6 +105,7 @@ from litellm.types.utils import (
 )
 from litellm.types.utils import Message as LitellmMessage
 from litellm.utils import (
+    EXTRA_BODY_ROUTING_KEYS,
     ModelResponse,
     Usage,
     add_dummy_tool,
@@ -165,6 +166,7 @@ _DEFER_LOADING_ADAPTER: Final = TypeAdapter(bool)
 _TOOL_FIELDS_ADAPTER: Final = TypeAdapter(Mapping[str, object])
 _TOOLS_ADAPTER: Final = TypeAdapter(list[object])
 _LITELLM_PARAMS_ADAPTER: Final = TypeAdapter(Mapping[str, object])
+_EXTRA_BODY_ADAPTER: Final = TypeAdapter(Mapping[str, object])
 _NATIVE_OUTPUT_STRING_FORMATS: Final = frozenset(
     ("date-time", "time", "date", "duration", "email", "hostname", "uri", "ipv4", "ipv6", "uuid")
 )
@@ -2418,6 +2420,7 @@ class AnthropicConfig(AnthropicModelInfo, BaseConfig):
         request_params: Final = cast(  # cast-ok: optional_params is the untyped dict of the shared transform signature
             dict[str, object], optional_params
         )
+        extra_body: Final = _EXTRA_BODY_ADAPTER.validate_python(request_params.pop("extra_body", None) or {})
         marked_tools: Final = tools_marked_for_a_tool_config_point(
             request_params.get("tools"), request_params.pop("cache_control_injection_points", None)
         )
@@ -2455,6 +2458,7 @@ class AnthropicConfig(AnthropicModelInfo, BaseConfig):
             "messages": anthropic_messages,
             **optional_params,
             **({} if marked_tools is None else {"tools": list(marked_tools)}),
+            **{k: v for k, v in extra_body.items() if k not in EXTRA_BODY_ROUTING_KEYS},
         }
 
         self._apply_output_config(data=data, model=model, optional_params=optional_params)

tests/unit/llms/anthropic/chat/test_anthropic_chat_handler.py

@@ -93,6 +93,47 @@ def test_anthropic_completion_does_not_send_deployment_default_limits():
     assert "default_api_key_tpm_limit" not in request_body
 
 
+def test_anthropic_completion_sends_extra_body_fields_top_level_without_redirecting_model():
+    captured_requests: list[httpx.Request] = []
+
+    def respond(request: httpx.Request) -> httpx.Response:
+        captured_requests.append(request)
+        return httpx.Response(
+            200,
+            json={
+                "id": "msg_extra_body",
+                "type": "message",
+                "role": "assistant",
+                "model": "claude-sonnet-5-5",
+                "content": [{"type": "text", "text": "Hello"}],
+                "stop_reason": "end_turn",
+                "stop_sequence": None,
+                "usage": {"input_tokens": 1, "output_tokens": 1},
+            },
+        )
+
+    client = HTTPHandler(client=httpx.Client(transport=httpx.MockTransport(respond)))
+    try:
+        litellm.completion(
+            model="anthropic/claude-sonnet-5-5",
+            messages=[{"role": "user", "content": "Hello"}],
+            api_key="test-key",
+            client=client,
+            max_tokens=16,
+            extra_body={"fallbacks": [{"model": "claude-opus-5-5"}], "model": "claude-opus-5-5"},
+        )
+    finally:
+        client.close()
+
+    request_body = json.loads(captured_requests[0].content)
+    assert request_body == {
+        "model": "claude-sonnet-5-5",
+        "messages": [{"role": "user", "content": [{"type": "text", "text": "Hello"}]}],
+        "max_tokens": 16,
+        "fallbacks": [{"model": "claude-opus-5-5"}],
+    }, request_body
+
+
 def test_anthropic_tool_history_without_tools_injects_a_dummy_tool(
     respx_mock: respx.MockRouter, monkeypatch: pytest.MonkeyPatch
 ) -> None:

tests/unit/test_anthropic_beta_headers_filtering.py

@@ -474,6 +474,25 @@ class TestAnthropicBetaHeadersFiltering:
 
         assert filtered == ["inline-tools-2026-09-15"]
 
+    @pytest.mark.parametrize(
+        ("provider", "expected"),
+        [
+            ("anthropic", ["server-side-fallback-2026-07-01"]),
+            ("vertex_ai", []),
+            ("bedrock", []),
+        ],
+    )
+    def test_server_side_fallback_forwarded_only_to_the_claude_api(self, provider: str, expected: list[str]) -> None:
+        """Anthropic rejects the `fallbacks` request field with 400 "fallbacks: Extra inputs are not permitted" unless
+        this beta is sent, and documents it for the Claude API only
+        (https://platform.claude.com/docs/en/build-with-claude/refusals-and-fallback, fetched 2026-10-26)"""
+        filtered: Final = filter_and_transform_beta_headers(
+            beta_headers=["server-side-fallback-2026-07-01"],
+            provider=provider,
+        )
+
+        assert filtered == expected
+
     def test_null_value_headers_filtered(self):
         """Test that headers with null values are always filtered out."""
         for provider in [