fix(native): preserve opaque metadata eligibility

litellm-rust/crates/core/src/chat_completions/mod.rs

@@ -84,8 +84,8 @@ fn unsupported_reason(
             "anthropic" => options
                 .anthropic
                 .as_ref()
-                .and_then(|anthropic| anthropic.user_id.as_ref())
-                .map(|_| Unsupported("LiteLLM user metadata")),
+                .is_some_and(|anthropic| anthropic.has_user_id)
+                .then_some(Unsupported("LiteLLM user metadata")),
             "bedrock" => options
                 .bedrock
                 .as_ref()

litellm-rust/crates/core/src/chat_completions/tests.rs

@@ -895,6 +895,7 @@ fn preflight_and_execution_share_provider_metadata_eligibility() {
                 custom_llm_provider: Some("anthropic".into()),
                 anthropic: Some(AnthropicOptions {
                     user_id: Some("u-123".into()),
+                    has_user_id: true,
                 }),
                 ..Default::default()
             },

litellm-rust/crates/core/src/request_options.rs

@@ -49,6 +49,7 @@ impl BedrockOptions {
 #[derive(Clone, Debug, Default)]
 pub struct AnthropicOptions {
     pub user_id: Option<String>,
+    pub has_user_id: bool,
 }
 
 #[derive(Clone, Debug, Default)]

litellm-rust/crates/python-bridge/src/marshal.rs

@@ -44,12 +44,14 @@ impl From<NativeBedrockOptions> for litellm_core::request_options::BedrockOption
 #[derive(FromPyObject)]
 struct NativeAnthropicOptions {
     user_id: Option<String>,
+    has_user_id: bool,
 }
 
 impl From<NativeAnthropicOptions> for litellm_core::request_options::AnthropicOptions {
     fn from(input: NativeAnthropicOptions) -> Self {
         Self {
             user_id: input.user_id,
+            has_user_id: input.has_user_id,
         }
     }
 }

litellm/rust_bridge/request.py

@@ -26,6 +26,7 @@ class NativeBedrockOptions:
 @dataclass(frozen=True, slots=True)
 class NativeAnthropicOptions:
     user_id: str | None = None
+    has_user_id: bool = False
 
 
 @dataclass(frozen=True, slots=True)
@@ -57,7 +58,10 @@ def bedrock_options(params: Mapping[str, object]) -> NativeBedrockOptions:
 def anthropic_options(litellm_params: Mapping[str, object] | None) -> NativeAnthropicOptions:
     metadata = None if litellm_params is None else litellm_params.get("metadata")
     user_id = metadata.get("user_id") if isinstance(metadata, Mapping) else None
-    return NativeAnthropicOptions(user_id=user_id if isinstance(user_id, str) else None)
+    return NativeAnthropicOptions(
+        user_id=user_id if isinstance(user_id, str) else None,
+        has_user_id=user_id is not None,
+    )
 
 
 def vertex_options(params: Mapping[str, object]) -> NativeVertexOptions:
@@ -68,6 +72,7 @@ def vertex_options(params: Mapping[str, object]) -> NativeVertexOptions:
         location=location if isinstance(location, str) else None,
     )
 
+
 from typing_extensions import ReadOnly, TypedDict
 
 

tests/test_litellm/anthropic_interface/test_rust_bridge_messages.py

@@ -254,6 +254,37 @@ async def test_public_messages_routes_provider_acceptance(monkeypatch, asynchron
     assert calls[0]["body"]["max_tokens"] == 64
 
 
+def test_public_messages_strips_provider_specific_fields_before_native_dispatch():
+    native = RecordingMessages()
+    litellm.rust(True)
+    rust_messages.set_rust_messages(messages=native)
+    messages = [
+        {
+            "role": "assistant",
+            "content": [
+                {
+                    "type": "tool_use",
+                    "id": "tool_1",
+                    "name": "lookup",
+                    "input": {},
+                    "provider_specific_fields": {"thought_signature": "signature"},
+                }
+            ],
+        }
+    ]
+
+    litellm.anthropic.messages.create(
+        model="anthropic/test-model",
+        max_tokens=64,
+        messages=messages,
+        api_key="key",
+    )
+
+    content = native.calls[0]["body"]["messages"][0]["content"][0]
+    assert "provider_specific_fields" not in content
+    assert "provider_specific_fields" in messages[0]["content"][0]
+
+
 @pytest.mark.parametrize("condition", ["disabled", "declined", "missing_binding", "missing_preflight", "stream"])
 def test_public_messages_fallback_once(monkeypatch, condition):
     module = importlib.import_module("litellm.llms.anthropic.experimental_pass_through.messages.handler")

tests/test_litellm/rust_bridge/test_chat_completions.py

@@ -477,6 +477,10 @@ def test_typed_capability_and_provider_metadata_facts_are_isolated():
     assert context.capabilities.request_format == "native"
     assert context.capabilities.has_agentic_hook is True
     assert anthropic.user_id == "user-123"
+    assert anthropic.has_user_id is True
+    assert anthropic_options({"metadata": {"user_id": object()}}).has_user_id is True
+    assert anthropic_options({"metadata": {"user_id": None}}).has_user_id is False
+
 
 @pytest.mark.parametrize("provider", ["anthropic", "bedrock", "openai"])
 @pytest.mark.parametrize("asynchronous", [False, True])