diff --git a/Cargo.toml b/Cargo.toml
index eb17994..9b3a503 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "agcore"
-version = "0.3.5"
+version = "0.3.6"
 edition = "2024"
 
 [features]
diff --git a/src/llm/provider/openai.rs b/src/llm/provider/openai.rs
index 42e5930..0f42b3e 100644
--- a/src/llm/provider/openai.rs
+++ b/src/llm/provider/openai.rs
@@ -242,6 +242,7 @@ pub(crate) struct OpenaiChatResponse {
     pub created: u64,
     pub model: String,
     pub choices: Vec<Choice>,
+    #[serde(default)]
     pub usage: crate::llm::types::usage::Usage,
     #[serde(skip_serializing_if = "Option::is_none")]
     pub system_fingerprint: Option<String>,
@@ -1968,4 +1969,49 @@ data: [DONE]\n\n";
             "非法 header 名应被静默跳过"
         );
     }
+
+    // ===== OpenaiChatResponse Usage 容错（v0.3.6 引入）=====
+
+    /// C1: Chat Completions 响应中 usage 键完全缺失 —— 默认 Usage::default()。
+    #[test]
+    fn deserialize_chat_response_missing_usage_key() {
+        let body: OpenaiChatResponse = serde_json::from_value(json!({
+            "id": "chatcmpl-test",
+            "object": "chat.completion",
+            "created": 1718000000,
+            "model": "gpt-4o",
+            "choices": [{
+                "index": 0,
+                "message": {"role": "assistant", "content": "hi"},
+                "finish_reason": "stop"
+            }]
+        }))
+        .unwrap();
+        assert_eq!(body.usage.prompt_tokens, 0);
+        assert_eq!(body.usage.completion_tokens, 0);
+        assert_eq!(body.usage.total_tokens, 0);
+        assert!(body.usage.completion_tokens_details.is_none());
+        assert!(body.usage.prompt_tokens_details.is_none());
+    }
+
+    /// C2: Chat Completions 响应中 usage 存在但缺子字段 —— 缺省字段默认 0。
+    #[test]
+    fn deserialize_chat_response_missing_usage_fields() {
+        let body: OpenaiChatResponse = serde_json::from_value(json!({
+            "id": "chatcmpl-test",
+            "object": "chat.completion",
+            "created": 1718000000,
+            "model": "gpt-4o",
+            "choices": [{
+                "index": 0,
+                "message": {"role": "assistant", "content": "hi"},
+                "finish_reason": "stop"
+            }],
+            "usage": {"prompt_tokens": 8}
+        }))
+        .unwrap();
+        assert_eq!(body.usage.prompt_tokens, 8);
+        assert_eq!(body.usage.completion_tokens, 0);
+        assert_eq!(body.usage.total_tokens, 0);
+    }
 }
diff --git a/src/llm/provider/openai_response.rs b/src/llm/provider/openai_response.rs
index 4650acc..a4d019a 100644
--- a/src/llm/provider/openai_response.rs
+++ b/src/llm/provider/openai_response.rs
@@ -204,6 +204,7 @@ pub(crate) struct OpenaiResponseBody {
     pub id: String,
     pub model: String,
     pub output: Vec<ResponseOutputItem>,
+    #[serde(default)]
     pub usage: Usage,
     pub status: String,
 }
@@ -2509,4 +2510,92 @@ data: {\"type\":\"response.failed\",\"error\":{\"message\":\"server failed mid-s
         let wire = serde_json::to_value(&tool).unwrap();
         assert_eq!(wire, original);
     }
+
+    // ===== Usage 字段容错（v0.3.6 引入）=====
+
+    /// U1: usage 子字段缺失 —— 缺失字段默认 0/None，结构体反序列化不报错。
+    #[test]
+    fn deserialize_missing_usage_fields() {
+        let body: OpenaiResponseBody = serde_json::from_value(json!({
+            "id": "r_1",
+            "model": "gpt-4o",
+            "output": [],
+            "usage": {"prompt_tokens": 5},
+            "status": "completed"
+        }))
+        .unwrap();
+        assert_eq!(body.usage.prompt_tokens, 5);
+        assert_eq!(body.usage.completion_tokens, 0);
+        assert_eq!(body.usage.total_tokens, 0);
+        assert!(body.usage.completion_tokens_details.is_none());
+        assert!(body.usage.prompt_tokens_details.is_none());
+    }
+
+    /// U2: usage 键完全缺失 —— OpenaiResponseBody.usage 默认 Usage::default()。
+    #[test]
+    fn deserialize_missing_usage_key() {
+        let body: OpenaiResponseBody = serde_json::from_value(json!({
+            "id": "r_1",
+            "model": "gpt-4o",
+            "output": [],
+            "status": "completed"
+        }))
+        .unwrap();
+        assert_eq!(body.usage.prompt_tokens, 0);
+        assert_eq!(body.usage.completion_tokens, 0);
+        assert_eq!(body.usage.total_tokens, 0);
+        assert!(body.usage.completion_tokens_details.is_none());
+        assert!(body.usage.prompt_tokens_details.is_none());
+    }
+
+    /// U3: usage 为空对象 —— 全字段走 Default，无 None panic。
+    #[test]
+    fn deserialize_empty_usage_object() {
+        let body: OpenaiResponseBody = serde_json::from_value(json!({
+            "id": "r_1",
+            "model": "gpt-4o",
+            "output": [],
+            "usage": {},
+            "status": "completed"
+        }))
+        .unwrap();
+        assert_eq!(body.usage.prompt_tokens, 0);
+        assert_eq!(body.usage.completion_tokens, 0);
+        assert_eq!(body.usage.total_tokens, 0);
+    }
+
+    /// U4: 完整 usage（含 details）回归 —— 确保 #[serde(default)] 不破坏正常路径。
+    #[test]
+    fn deserialize_full_usage_with_details() {
+        let body: OpenaiResponseBody = serde_json::from_value(json!({
+            "id": "r_1",
+            "model": "gpt-4o",
+            "output": [],
+            "usage": {
+                "prompt_tokens": 10,
+                "completion_tokens": 20,
+                "total_tokens": 30,
+                "completion_tokens_details": {"reasoning_tokens": 5}
+            },
+            "status": "completed"
+        }))
+        .unwrap();
+        assert_eq!(body.usage.prompt_tokens, 10);
+        assert_eq!(body.usage.completion_tokens, 20);
+        assert_eq!(body.usage.total_tokens, 30);
+        let details = body.usage.completion_tokens_details.unwrap();
+        assert_eq!(details.reasoning_tokens, Some(5));
+    }
+
+    /// U5: OpenaiResponseBody 上下文中 usage key 完全缺失 —— 与 U2 同场景但明确命名。
+    #[test]
+    fn deserialize_response_body_missing_usage_key() {
+        let json_text = r#"{"id":"r_1","model":"gpt-4o","output":[],"status":"completed"}"#;
+        let body: OpenaiResponseBody = serde_json::from_str(json_text).unwrap();
+        assert_eq!(body.usage.prompt_tokens, 0);
+        assert_eq!(body.usage.completion_tokens, 0);
+        assert_eq!(body.usage.total_tokens, 0);
+        assert!(body.usage.completion_tokens_details.is_none());
+        assert!(body.usage.prompt_tokens_details.is_none());
+    }
 }
diff --git a/src/llm/types/usage.rs b/src/llm/types/usage.rs
index fbeb44c..84689e4 100644
--- a/src/llm/types/usage.rs
+++ b/src/llm/types/usage.rs
@@ -1,6 +1,7 @@
 use serde::{Deserialize, Serialize};
 
 #[derive(Debug, Clone, Copy, Default, Serialize, Deserialize)]
+#[serde(default)]
 pub struct Usage {
     pub prompt_tokens: u32,
     pub completion_tokens: u32,
@@ -79,3 +80,33 @@ impl Usage {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use serde_json::json;
+
+    #[test]
+    fn deserialize_usage_missing_prompt_tokens() {
+        let value = json!({
+            "completion_tokens": 5,
+            "total_tokens": 5
+        });
+        let usage: Usage = serde_json::from_value(value).unwrap();
+        assert_eq!(usage.prompt_tokens, 0);
+        assert_eq!(usage.completion_tokens, 5);
+        assert_eq!(usage.total_tokens, 5);
+    }
+
+    #[test]
+    fn serialize_deserialize_roundtrip() {
+        let original = Usage::from_input_output(10, 20);
+        let serialized = serde_json::to_value(original).unwrap();
+        let deserialized: Usage = serde_json::from_value(serialized).unwrap();
+        assert_eq!(deserialized.prompt_tokens, original.prompt_tokens);
+        assert_eq!(deserialized.completion_tokens, original.completion_tokens);
+        assert_eq!(deserialized.total_tokens, original.total_tokens);
+        assert!(deserialized.completion_tokens_details.is_none());
+        assert!(deserialized.prompt_tokens_details.is_none());
+    }
+}