diff --git a/src-tauri/src/proxy/providers/streaming.rs b/src-tauri/src/proxy/providers/streaming.rs
index 725255d1..e923537f 100644
--- a/src-tauri/src/proxy/providers/streaming.rs
+++ b/src-tauri/src/proxy/providers/streaming.rs
@@ -112,6 +112,28 @@ fn build_anthropic_usage_json(usage: &Usage) -> Value {
     usage_json
 }
 
+fn default_anthropic_usage_json() -> Value {
+    json!({
+        "input_tokens": 0,
+        "output_tokens": 0
+    })
+}
+
+fn build_message_delta_event(stop_reason: Option<String>, usage_json: Option<Value>) -> Value {
+    let usage = usage_json
+        .filter(|usage| usage.is_object())
+        .unwrap_or_else(default_anthropic_usage_json);
+
+    json!({
+        "type": "message_delta",
+        "delta": {
+            "stop_reason": stop_reason,
+            "stop_sequence": null
+        },
+        "usage": usage
+    })
+}
+
 /// 创建 Anthropic SSE 流
 pub fn create_anthropic_sse_stream<E: std::error::Error + Send + 'static>(
     stream: impl Stream<Item = Result<Bytes, E>> + Send + 'static,
@@ -157,16 +179,7 @@ pub fn create_anthropic_sse_stream<E: std::error::Error + Send + 'static>(
 
                                     // 流正常结束，发出缓存的 message_delta（含完整 usage）。
                                     if let Some((stop_reason, usage_json)) = pending_message_delta.take() {
-                                        let mut event = json!({
-                                            "type": "message_delta",
-                                            "delta": {
-                                                "stop_reason": stop_reason,
-                                                "stop_sequence": null
-                                            }
-                                        });
-                                        if let Some(uj) = usage_json {
-                                            event["usage"] = uj;
-                                        }
+                                        let event = build_message_delta_event(stop_reason, usage_json);
                                         let sse_data = format!("event: message_delta\ndata: {}\n\n",
                                             serde_json::to_string(&event).unwrap_or_default());
                                         log::debug!("[Claude/OpenRouter] >>> Anthropic SSE: message_delta (from pending)");
@@ -616,16 +629,7 @@ pub fn create_anthropic_sse_stream<E: std::error::Error + Send + 'static>(
             let emitted_pending_message_delta = if let Some((stop_reason, usage_json)) =
                 pending_message_delta.take()
             {
-                let mut event = json!({
-                    "type": "message_delta",
-                    "delta": {
-                        "stop_reason": stop_reason,
-                        "stop_sequence": null
-                    }
-                });
-                if let Some(uj) = usage_json {
-                    event["usage"] = uj;
-                }
+                let event = build_message_delta_event(stop_reason, usage_json);
                 let sse_data = format!("event: message_delta\ndata: {}\n\n",
                     serde_json::to_string(&event).unwrap_or_default());
                 log::debug!("[Claude/OpenRouter] >>> Anthropic SSE: message_delta (at stream end)");
@@ -1031,6 +1035,42 @@ mod tests {
         );
     }
 
+    #[tokio::test]
+    async fn test_message_delta_includes_zero_usage_when_stream_has_no_usage() {
+        let input = concat!(
+            "data: {\"id\":\"chatcmpl_no_usage\",\"model\":\"gpt-5.5\",\"choices\":[{\"delta\":{\"tool_calls\":[{\"index\":0,\"id\":\"call_0\",\"type\":\"function\",\"function\":{\"name\":\"get_time\",\"arguments\":\"{}\"}}]}}]}\n\n",
+            "data: {\"id\":\"chatcmpl_no_usage\",\"model\":\"gpt-5.5\",\"choices\":[{\"delta\":{},\"finish_reason\":\"tool_calls\"}]}\n\n",
+            "data: [DONE]\n\n"
+        );
+
+        let events = collect_anthropic_events(input).await;
+        let message_deltas: Vec<&Value> = events
+            .iter()
+            .filter(|event| event_type(event) == Some("message_delta"))
+            .collect();
+
+        assert_eq!(message_deltas.len(), 1);
+        let message_delta = message_deltas[0];
+        assert_eq!(
+            message_delta
+                .pointer("/delta/stop_reason")
+                .and_then(|v| v.as_str()),
+            Some("tool_use")
+        );
+        assert_eq!(
+            message_delta
+                .pointer("/usage/input_tokens")
+                .and_then(|v| v.as_u64()),
+            Some(0)
+        );
+        assert_eq!(
+            message_delta
+                .pointer("/usage/output_tokens")
+                .and_then(|v| v.as_u64()),
+            Some(0)
+        );
+    }
+
     #[tokio::test]
     async fn test_streaming_finalizes_after_finish_when_done_is_missing() {
         let input = concat!(