fix: normalize Anthropic model routing

rust/crates/api/src/providers/anthropic.rs

@@ -468,8 +468,7 @@ impl AnthropicClient {
         request: &MessageRequest,
     ) -> Result<reqwest::Response, ApiError> {
         let request_url = format!("{}/v1/messages", self.base_url.trim_end_matches('/'));
-        let mut request_body = self.request_profile.render_json_body(request)?;
-        strip_unsupported_beta_body_fields(&mut request_body);
+        let request_body = render_standard_messages_body(&self.request_profile, request)?;
         let request_builder = self.build_request(&request_url).json(&request_body);
         request_builder.send().await.map_err(ApiError::from)
     }
@@ -529,8 +528,7 @@ impl AnthropicClient {
             "{}/v1/messages/count_tokens",
             self.base_url.trim_end_matches('/')
         );
-        let mut request_body = self.request_profile.render_json_body(request)?;
-        strip_unsupported_beta_body_fields(&mut request_body);
+        let request_body = render_standard_messages_body(&self.request_profile, request)?;
         let response = self
             .build_request(&request_url)
             .json(&request_body)
@@ -977,6 +975,21 @@ fn enrich_bearer_auth_error(error: ApiError, auth: &AuthSource) -> ApiError {
     }
 }
 
+fn anthropic_wire_model(model: &str) -> &str {
+    model.strip_prefix("anthropic/").unwrap_or(model)
+}
+
+fn render_standard_messages_body(
+    request_profile: &AnthropicRequestProfile,
+    request: &MessageRequest,
+) -> Result<Value, serde_json::Error> {
+    let mut wire_request = request.clone();
+    wire_request.model = anthropic_wire_model(&request.model).to_string();
+    let mut body = request_profile.render_json_body(&wire_request)?;
+    strip_unsupported_beta_body_fields(&mut body);
+    Ok(body)
+}
+
 /// Remove beta-only body fields that the standard `/v1/messages` and
 /// `/v1/messages/count_tokens` endpoints reject as `Extra inputs are not
 /// permitted`. The `betas` opt-in is communicated via the `anthropic-beta`
@@ -1550,6 +1563,27 @@ mod tests {
         );
     }
 
+    #[test]
+    fn standard_messages_body_strips_anthropic_routing_prefix() {
+        let client = AnthropicClient::new("test-key");
+        let request = MessageRequest {
+            model: "anthropic/claude-opus-4-6".to_string(),
+            max_tokens: 64,
+            messages: vec![],
+            system: None,
+            tools: None,
+            tool_choice: None,
+            stream: false,
+            ..Default::default()
+        };
+
+        let rendered = super::render_standard_messages_body(client.request_profile(), &request)
+            .expect("body should render");
+
+        assert_eq!(rendered["model"], serde_json::json!("claude-opus-4-6"));
+        assert!(rendered.get("betas").is_none());
+    }
+
     #[test]
     fn enrich_bearer_auth_error_appends_sk_ant_hint_on_401_with_pure_bearer_token() {
         // given

rust/crates/api/tests/client_integration.rs

@@ -103,6 +103,58 @@ async fn send_message_posts_json_and_parses_response() {
     );
 }
 
+#[tokio::test]
+async fn send_message_strips_anthropic_routing_prefix_on_wire() {
+    let state = Arc::new(Mutex::new(Vec::<CapturedRequest>::new()));
+    let server = spawn_server(
+        state.clone(),
+        vec![
+            http_response("200 OK", "application/json", "{\"input_tokens\":1}"),
+            http_response(
+                "200 OK",
+                "application/json",
+                concat!(
+                    "{",
+                    "\"id\":\"msg_prefixed\",",
+                    "\"type\":\"message\",",
+                    "\"role\":\"assistant\",",
+                    "\"content\":[{\"type\":\"text\",\"text\":\"ok\"}],",
+                    "\"model\":\"claude-opus-4-6\",",
+                    "\"stop_reason\":\"end_turn\",",
+                    "\"stop_sequence\":null,",
+                    "\"usage\":{\"input_tokens\":1,\"output_tokens\":1}",
+                    "}"
+                ),
+            ),
+        ],
+    )
+    .await;
+
+    let client = AnthropicClient::new("test-key").with_base_url(server.base_url());
+    client
+        .send_message(&MessageRequest {
+            model: "anthropic/claude-opus-4-6".to_string(),
+            ..sample_request(false)
+        })
+        .await
+        .expect("request should succeed");
+
+    let captured = state.lock().await;
+    assert_eq!(
+        captured.len(),
+        2,
+        "count_tokens and messages requests should be captured"
+    );
+    let count_tokens_body: serde_json::Value =
+        serde_json::from_str(&captured[0].body).expect("count_tokens body should be json");
+    let messages_body: serde_json::Value =
+        serde_json::from_str(&captured[1].body).expect("request body should be json");
+    assert_eq!(captured[0].path, "/v1/messages/count_tokens");
+    assert_eq!(captured[1].path, "/v1/messages");
+    assert_eq!(count_tokens_body["model"], json!("claude-opus-4-6"));
+    assert_eq!(messages_body["model"], json!("claude-opus-4-6"));
+}
+
 #[tokio::test]
 async fn send_message_blocks_oversized_requests_before_the_http_call() {
     let state = Arc::new(Mutex::new(Vec::<CapturedRequest>::new()));