diff --git a/apps/api/src/services/nvidia_provider.py b/apps/api/src/services/nvidia_provider.py
index 162e53ab4..5dd279d88 100644
--- a/apps/api/src/services/nvidia_provider.py
+++ b/apps/api/src/services/nvidia_provider.py
@@ -780,6 +780,20 @@ class NvidiaProvider:
                     logger.warning("nvidia_chat_timeout", error=str(e))
                     return f"Timeout: {e}", False, 0, 0.0
 
+                except httpx.HTTPStatusError as e:
+                    # 2026-03-31 ogt: 記錄完整響應體以診斷 400 錯誤
+                    self._circuit_breaker.record_failure()
+                    NVIDIA_REQUESTS_TOTAL.labels(status="error", tool_name="chat").inc()
+                    response_text = e.response.text if e.response else "No response body"
+                    logger.warning(
+                        "nvidia_chat_failed",
+                        error=str(e),
+                        error_type="HTTPStatusError",
+                        status_code=e.response.status_code if e.response else None,
+                        response_body=response_text[:500],  # 截斷避免日誌過大
+                    )
+                    return str(e), False, 0, 0.0
+
                 except Exception as e:
                     self._circuit_breaker.record_failure()
                     NVIDIA_REQUESTS_TOTAL.labels(status="error", tool_name="chat").inc()