diff --git a/rust/crates/api/benches/request_building.rs b/rust/crates/api/benches/request_building.rs
index 23493477..c0d97c96 100644
--- a/rust/crates/api/benches/request_building.rs
+++ b/rust/crates/api/benches/request_building.rs
@@ -38,6 +38,7 @@ fn create_sample_request(message_count: usize) -> MessageRequest {
                         id: format!("call_{}", i),
                         name: "read_file".to_string(),
                         input: json!({"path": format!("/tmp/file{}", i)}),
+                        thought_signature: None,
                     },
                 ],
             }),
@@ -57,6 +58,7 @@ fn create_sample_request(message_count: usize) -> MessageRequest {
                     id: format!("call_{}", i),
                     name: "write_file".to_string(),
                     input: json!({"path": format!("/tmp/out{}", i), "content": "data"}),
+                    thought_signature: None,
                 }],
             }),
         }
@@ -105,11 +107,13 @@ fn bench_translate_message(c: &mut Criterion) {
                 id: "call_1".to_string(),
                 name: "read_file".to_string(),
                 input: json!({"path": "/tmp/test"}),
+                thought_signature: None,
             },
             InputContentBlock::ToolUse {
                 id: "call_2".to_string(),
                 name: "write_file".to_string(),
                 input: json!({"path": "/tmp/out", "content": "data"}),
+                thought_signature: None,
             },
         ],
     };
diff --git a/rust/crates/api/src/providers/openai_compat.rs b/rust/crates/api/src/providers/openai_compat.rs
index cb6b329e..b10e737b 100644
--- a/rust/crates/api/src/providers/openai_compat.rs
+++ b/rust/crates/api/src/providers/openai_compat.rs
@@ -586,6 +586,21 @@ impl StreamState {
                 }
             }
 
+            if let Some(delta_extra) = &choice.delta.extra_content {
+                if let Some(delta_sig) = delta_extra
+                    .get("google")
+                    .and_then(|g| g.get("thought_signature"))
+                    .and_then(|v| v.as_str())
+                    .filter(|s| !s.is_empty())
+                {
+                    for state in self.tool_calls.values_mut() {
+                        if state.thought_signature.is_none() {
+                            state.thought_signature.get_or_insert(delta_sig.to_string());
+                        }
+                    }
+                }
+            }
+
             if let Some(finish_reason) = choice.finish_reason {
                 self.stop_reason = Some(normalize_finish_reason(&finish_reason));
                 if finish_reason == "tool_calls" {
@@ -693,6 +708,7 @@ struct ToolCallState {
     id: Option<String>,
     name: Option<String>,
     arguments: String,
+    thought_signature: Option<String>,
     emitted_len: usize,
     started: bool,
     stopped: bool,
@@ -710,6 +726,24 @@ impl ToolCallState {
         if let Some(arguments) = tool_call.function.arguments {
             self.arguments.push_str(&arguments);
         }
+
+        if let Some(sig) = tool_call.thought_signature.filter(|s| !s.is_empty()) {
+            self.thought_signature.get_or_insert(sig);
+        }
+
+        // https://ai.google.dev/gemini-api/docs/thought-signatures
+        if self.thought_signature.is_none() {
+            if let Some(sig) = tool_call
+                .extra_content
+                .as_ref()
+                .and_then(|ec| ec.get("google"))
+                .and_then(|g| g.get("thought_signature"))
+                .and_then(|v| v.as_str())
+                .filter(|s| !s.is_empty())
+            {
+                self.thought_signature.get_or_insert(sig.to_string());
+            }
+        }
     }
 
     const fn block_index(&self, offset: u32) -> u32 {
@@ -731,6 +765,7 @@ impl ToolCallState {
                 id,
                 name,
                 input: json!({}),
+                thought_signature: self.thought_signature.clone(),
             },
         }))
     }
@@ -782,6 +817,10 @@ struct ChatMessage {
 struct ResponseToolCall {
     id: String,
     function: ResponseToolFunction,
+    #[serde(default)]
+    thought_signature: Option<String>,
+    #[serde(default)]
+    extra_content: Option<serde_json::Value>,
 }
 
 #[derive(Debug, Deserialize)]
@@ -852,6 +891,8 @@ struct ChunkDelta {
     thinking: Option<ThinkingDelta>,
     #[serde(default, deserialize_with = "deserialize_null_as_empty_vec")]
     tool_calls: Vec<DeltaToolCall>,
+    #[serde(default)]
+    extra_content: Option<serde_json::Value>,
 }
 
 #[derive(Debug, Default, Deserialize)]
@@ -860,7 +901,7 @@ struct ThinkingDelta {
     content: Option<String>,
 }
 
-#[derive(Debug, Deserialize)]
+#[derive(Debug, Default, Deserialize)]
 struct DeltaToolCall {
     #[serde(default)]
     index: u32,
@@ -868,6 +909,10 @@ struct DeltaToolCall {
     id: Option<String>,
     #[serde(default)]
     function: DeltaFunction,
+    #[serde(default)]
+    thought_signature: Option<String>,
+    #[serde(default)]
+    extra_content: Option<serde_json::Value>,
 }
 
 #[derive(Debug, Default, Deserialize)]
@@ -923,6 +968,22 @@ pub fn model_requires_reasoning_content_in_history(model: &str) -> bool {
     canonical.starts_with("deepseek-v4")
 }
 
+/// Dummy thought signature accepted by Gemini as a validation bypass for
+/// conversation history that lacks a real signature. Source:
+/// - LiteLLM: https://github.com/BerriAI/litellm/pull/16812
+/// - Google: https://ai.google.dev/gemini-api/docs/thought-signatures#faqs
+const GEMINI_DUMMY_THOUGHT_SIGNATURE: &str = "c2tpcF90aG91Z2h0X3NpZ25hdHVyZV92YWxpZGF0b3I=";
+
+/// Returns true if the model is a Gemini model (Gemini 2.5+, 3+ etc) that
+/// requires `thought_signature` on function calls in conversation history.
+#[must_use]
+pub fn is_gemini_model(model: &str) -> bool {
+    let lowered = model.to_ascii_lowercase();
+    let canonical = lowered.rsplit('/').next().unwrap_or(lowered.as_str());
+    canonical.starts_with("gemini")
+}
+
+
 /// Strip routing prefix (e.g., "openai/gpt-4" → "gpt-4") for the wire.
 /// The prefix is used only to select transport; the backend expects the
 /// bare model id. Use `local/` to force OpenAI-compatible routing while
@@ -1216,14 +1277,32 @@ pub fn translate_message(message: &InputMessage, model: &str) -> Vec<Value> {
                     InputContentBlock::Thinking {
                         thinking: value, ..
                     } => reasoning.push_str(value),
-                    InputContentBlock::ToolUse { id, name, input } => tool_calls.push(json!({
-                        "id": id,
-                        "type": "function",
-                        "function": {
-                            "name": name,
-                            "arguments": input.to_string(),
+                    InputContentBlock::ToolUse { id, name, input, thought_signature } => {
+                        let mut tc = json!({
+                            "id": id,
+                            "type": "function",
+                            "function": {
+                                "name": name,
+                                "arguments": input.to_string(),
+                            }
+                        });
+
+                        let sig_for_gemini = thought_signature.clone().or_else(|| {
+                            if is_gemini_model(model) {
+                                Some(GEMINI_DUMMY_THOUGHT_SIGNATURE.to_string())
+                            } else {
+                                None
+                            }
+                        });
+                        if let Some(sig) = sig_for_gemini {
+                            tc["extra_content"] = json!({
+                                "google": {
+                                    "thought_signature": sig
+                                }
+                            });
                         }
-                    })),
+                        tool_calls.push(tc);
+                    }
                     InputContentBlock::ToolResult { .. } => {}
                 }
             }
@@ -1468,10 +1547,22 @@ fn normalize_response(
         content.push(OutputContentBlock::Text { text });
     }
     for tool_call in choice.message.tool_calls {
+        let thought_signature = tool_call.thought_signature.or_else(|| {
+            tool_call
+                .extra_content
+                .as_ref()
+                .and_then(|ec| ec.get("google"))
+                .and_then(|g| g.get("thought_signature"))
+                .and_then(|v| v.as_str())
+                .filter(|s| !s.is_empty())
+                .map(String::from)
+        });
+
         content.push(OutputContentBlock::ToolUse {
             id: tool_call.id,
             name: tool_call.function.name,
             input: parse_tool_arguments(&tool_call.function.arguments),
+            thought_signature,
         });
     }
 
@@ -1866,6 +1957,7 @@ mod tests {
                     id: "call_1".to_string(),
                     name: "get_weather".to_string(),
                     input: json!({"city": "Paris"}),
+                    thought_signature: None,
                 }],
             }],
             stream: false,
@@ -1943,6 +2035,7 @@ mod tests {
                         reasoning_content: Some("think".to_string()),
                         thinking: None,
                         tool_calls: Vec::new(),
+                        extra_content: None,
                     },
                     finish_reason: None,
                 }],
@@ -1960,6 +2053,7 @@ mod tests {
                             reasoning_content: None,
                             thinking: None,
                             tool_calls: Vec::new(),
+                            extra_content: None,
                         },
                         finish_reason: Some("stop".to_string()),
                     }],
@@ -2504,6 +2598,7 @@ mod tests {
                     id: "call_1".to_string(),
                     name: "read_file".to_string(),
                     input: serde_json::json!({"path": "/tmp/test"}),
+                    thought_signature: None,
                 }],
             }],
             stream: false,
@@ -2722,6 +2817,7 @@ mod tests {
                         id: "call_1".to_string(),
                         name: "read_file".to_string(),
                         input: serde_json::json!({"path": "/tmp/test"}),
+                        thought_signature: None,
                     }],
                 },
                 InputMessage {
diff --git a/rust/crates/api/src/types.rs b/rust/crates/api/src/types.rs
index 3ec7f879..adc5f4dc 100644
--- a/rust/crates/api/src/types.rs
+++ b/rust/crates/api/src/types.rs
@@ -100,6 +100,8 @@ pub enum InputContentBlock {
         id: String,
         name: String,
         input: Value,
+        #[serde(default, skip_serializing_if = "Option::is_none")]
+        thought_signature: Option<String>,
     },
     ToolResult {
         tool_use_id: String,
@@ -167,6 +169,8 @@ pub enum OutputContentBlock {
         id: String,
         name: String,
         input: Value,
+        #[serde(default, skip_serializing_if = "Option::is_none")]
+        thought_signature: Option<String>,
     },
     Thinking {
         #[serde(default)]
diff --git a/rust/crates/claw-analog/src/lib.rs b/rust/crates/claw-analog/src/lib.rs
index 33e4863f..5fbfe4ee 100644
--- a/rust/crates/claw-analog/src/lib.rs
+++ b/rust/crates/claw-analog/src/lib.rs
@@ -768,7 +768,7 @@ fn tool_calls_for_json(content: &[OutputContentBlock]) -> Vec<Value> {
     content
         .iter()
         .filter_map(|b| {
-            if let OutputContentBlock::ToolUse { id, name, input } = b {
+            if let OutputContentBlock::ToolUse { id, name, input, .. } = b {
                 Some(json!({
                     "id": id,
                     "name": name,
@@ -1474,7 +1474,7 @@ async fn stream_to_message_response(
                     block_kind.insert(index, BlockKind::Text);
                     text_buf.insert(index, text);
                 }
-                OutputContentBlock::ToolUse { id, name, input } => {
+                OutputContentBlock::ToolUse { id, name, input, .. } => {
                     let json = if input.as_object().is_some_and(|m| m.is_empty()) {
                         String::new()
                     } else {
@@ -1523,7 +1523,7 @@ async fn stream_to_message_response(
                     Some(BlockKind::Tool { id, name, json }) => {
                         let input = serde_json::from_str::<Value>(&json)
                             .unwrap_or_else(|_| json!({ "raw": json }));
-                        finished.insert(idx, OutputContentBlock::ToolUse { id, name, input });
+                        finished.insert(idx, OutputContentBlock::ToolUse { id, name, input, thought_signature: None });
                     }
                     None => {}
                 }
@@ -1581,7 +1581,7 @@ fn collect_tool_uses(content: &[OutputContentBlock]) -> Vec<ToolUse<'_>> {
     content
         .iter()
         .filter_map(|b| {
-            if let OutputContentBlock::ToolUse { id, name, input } = b {
+            if let OutputContentBlock::ToolUse { id, name, input, .. } = b {
                 Some(ToolUse {
                     id: id.as_str(),
                     name: name.as_str(),
@@ -1601,10 +1601,11 @@ fn output_to_input_blocks(blocks: &[OutputContentBlock]) -> Vec<InputContentBloc
             OutputContentBlock::Text { text } => {
                 Some(InputContentBlock::Text { text: text.clone() })
             }
-            OutputContentBlock::ToolUse { id, name, input } => Some(InputContentBlock::ToolUse {
+            OutputContentBlock::ToolUse { id, name, input, .. } => Some(InputContentBlock::ToolUse {
                 id: id.clone(),
                 name: name.clone(),
                 input: input.clone(),
+                thought_signature: None,
             }),
             OutputContentBlock::Thinking { .. } | OutputContentBlock::RedactedThinking { .. } => {
                 None
diff --git a/rust/crates/mock-anthropic-service/src/lib.rs b/rust/crates/mock-anthropic-service/src/lib.rs
index 68968eed..85f3e856 100644
--- a/rust/crates/mock-anthropic-service/src/lib.rs
+++ b/rust/crates/mock-anthropic-service/src/lib.rs
@@ -746,6 +746,7 @@ fn tool_message_response_many(id: &str, tool_uses: &[ToolUseMessage<'_>]) -> Mes
                 id: tool_use.tool_id.to_string(),
                 name: tool_use.tool_name.to_string(),
                 input: tool_use.input.clone(),
+                thought_signature: None,
             })
             .collect(),
         model: DEFAULT_MODEL.to_string(),
diff --git a/rust/crates/runtime/src/compact.rs b/rust/crates/runtime/src/compact.rs
index 797d3a6b..42f23015 100644
--- a/rust/crates/runtime/src/compact.rs
+++ b/rust/crates/runtime/src/compact.rs
@@ -780,6 +780,7 @@ mod tests {
                     id: tool_id.to_string(),
                     name: "search".to_string(),
                     input: "{\"q\":\"*.rs\"}".to_string(),
+                    thought_signature: None,
                 },
             ]))
             .unwrap();
diff --git a/rust/crates/runtime/src/conversation.rs b/rust/crates/runtime/src/conversation.rs
index ea50e3bd..fe636f8f 100644
--- a/rust/crates/runtime/src/conversation.rs
+++ b/rust/crates/runtime/src/conversation.rs
@@ -37,6 +37,7 @@ pub enum AssistantEvent {
         id: String,
         name: String,
         input: String,
+        thought_signature: Option<String>,
     },
     Usage(TokenUsage),
     PromptCache(PromptCacheEvent),
@@ -381,7 +382,7 @@ where
                 .blocks
                 .iter()
                 .filter_map(|block| match block {
-                    ContentBlock::ToolUse { id, name, input } => {
+                    ContentBlock::ToolUse { id, name, input, .. } => {
                         Some((id.clone(), name.clone(), input.clone()))
                     }
                     _ => None,
@@ -741,9 +742,9 @@ fn build_assistant_message(
                 });
             }
             AssistantEvent::TextDelta(delta) => text.push_str(&delta),
-            AssistantEvent::ToolUse { id, name, input } => {
+            AssistantEvent::ToolUse { id, name, input, thought_signature } => {
                 flush_text_block(&mut text, &mut blocks);
-                blocks.push(ContentBlock::ToolUse { id, name, input });
+                blocks.push(ContentBlock::ToolUse { id, name, input, thought_signature });
             }
             AssistantEvent::Usage(value) => usage = Some(value),
             AssistantEvent::PromptCache(event) => prompt_cache_events.push(event),
@@ -880,6 +881,7 @@ mod tests {
                             id: "tool-1".to_string(),
                             name: "add".to_string(),
                             input: "2,2".to_string(),
+                            thought_signature: None,
                         },
                         AssistantEvent::Usage(TokenUsage {
                             input_tokens: 20,
@@ -1046,6 +1048,7 @@ mod tests {
                         id: "tool-1".to_string(),
                         name: "blocked".to_string(),
                         input: "secret".to_string(),
+                        thought_signature: None,
                     },
                     AssistantEvent::MessageStop,
                 ])
@@ -1091,6 +1094,7 @@ mod tests {
                         id: "tool-1".to_string(),
                         name: "blocked".to_string(),
                         input: r#"{"path":"secret.txt"}"#.to_string(),
+                        thought_signature: None,
                     },
                     AssistantEvent::MessageStop,
                 ])
@@ -1153,6 +1157,7 @@ mod tests {
                         id: "tool-1".to_string(),
                         name: "blocked".to_string(),
                         input: r#"{"path":"secret.txt"}"#.to_string(),
+                        thought_signature: None,
                     },
                     AssistantEvent::MessageStop,
                 ])
@@ -1213,6 +1218,7 @@ mod tests {
                             id: "tool-1".to_string(),
                             name: "add".to_string(),
                             input: r#"{"lhs":2,"rhs":2}"#.to_string(),
+                            thought_signature: None,
                         },
                         AssistantEvent::MessageStop,
                     ]),
@@ -1288,6 +1294,7 @@ mod tests {
                             id: "tool-1".to_string(),
                             name: "fail".to_string(),
                             input: r#"{"path":"README.md"}"#.to_string(),
+                            thought_signature: None,
                         },
                         AssistantEvent::MessageStop,
                     ]),
@@ -1755,6 +1762,7 @@ mod tests {
                 id: "tool-1".to_string(),
                 name: "echo".to_string(),
                 input: "payload".to_string(),
+                thought_signature: None,
             },
             AssistantEvent::MessageStop,
         ];
@@ -1778,6 +1786,7 @@ mod tests {
                     id: "tool-1".to_string(),
                     name: "echo".to_string(),
                     input: "payload".to_string(),
+                    thought_signature: None,
                 },
             ]
         );
@@ -1811,6 +1820,7 @@ mod tests {
                         id: "tool-1".to_string(),
                         name: "echo".to_string(),
                         input: "payload".to_string(),
+                        thought_signature: None,
                     },
                     AssistantEvent::MessageStop,
                 ])
diff --git a/rust/crates/runtime/src/session.rs b/rust/crates/runtime/src/session.rs
index 0cc32c03..620c748c 100644
--- a/rust/crates/runtime/src/session.rs
+++ b/rust/crates/runtime/src/session.rs
@@ -42,6 +42,7 @@ pub enum ContentBlock {
         id: String,
         name: String,
         input: String,
+        thought_signature: Option<String>,
     },
     ToolResult {
         tool_use_id: String,
@@ -817,7 +818,7 @@ impl ContentBlock {
                     );
                 }
             }
-            Self::ToolUse { id, name, input } => {
+            Self::ToolUse { id, name, input, thought_signature } => {
                 object.insert(
                     "type".to_string(),
                     JsonValue::String("tool_use".to_string()),
@@ -825,6 +826,12 @@ impl ContentBlock {
                 object.insert("id".to_string(), JsonValue::String(id.clone()));
                 object.insert("name".to_string(), JsonValue::String(name.clone()));
                 object.insert("input".to_string(), JsonValue::String(input.clone()));
+                if let Some(sig) = thought_signature {
+                    object.insert(
+                        "thought_signature".to_string(),
+                        JsonValue::String(sig.clone()),
+                    );
+                }
             }
             Self::ToolResult {
                 tool_use_id,
@@ -874,6 +881,7 @@ impl ContentBlock {
                 id: required_string(object, "id")?,
                 name: required_string(object, "name")?,
                 input: required_string(object, "input")?,
+                thought_signature: object.get("thought_signature").and_then(JsonValue::as_str).map(String::from)
             }),
             "tool_result" => Ok(Self::ToolResult {
                 tool_use_id: required_string(object, "tool_use_id")?,
@@ -1069,7 +1077,7 @@ fn persisted_block_json(block: &ContentBlock) -> JsonValue {
                 );
             }
         }
-        ContentBlock::ToolUse { id, name, input } => {
+        ContentBlock::ToolUse { id, name, input, thought_signature } => {
             object.insert(
                 "type".to_string(),
                 JsonValue::String("tool_use".to_string()),
@@ -1083,6 +1091,12 @@ fn persisted_block_json(block: &ContentBlock) -> JsonValue {
                 "input".to_string(),
                 JsonValue::String(sanitize_jsonl_field(input)),
             );
+            if let Some(sig) = thought_signature {
+                object.insert(
+                    "thought_signature".to_string(),
+                    JsonValue::String(sanitize_jsonl_field(sig)),
+                );
+            }
         }
         ContentBlock::ToolResult {
             tool_use_id,
@@ -1433,6 +1447,7 @@ mod tests {
                         id: "tool-1".to_string(),
                         name: "bash".to_string(),
                         input: "echo hi".to_string(),
+                        thought_signature: None,
                     },
                 ],
                 Some(TokenUsage {
@@ -1596,6 +1611,7 @@ mod tests {
                     id: "tool-1".to_string(),
                     name: "bash".to_string(),
                     input: format!("Authorization: Bearer {secret}"),
+                    thought_signature: None,
                 },
             ]))
             .expect("tool use should append");
diff --git a/rust/crates/runtime/src/trident.rs b/rust/crates/runtime/src/trident.rs
index 2346a4ea..e09ef09d 100644
--- a/rust/crates/runtime/src/trident.rs
+++ b/rust/crates/runtime/src/trident.rs
@@ -686,6 +686,7 @@ mod tests {
                 id: "1".to_string(),
                 name: "read_file".to_string(),
                 input: r#"{"path":"src/main.rs"}"#.to_string(),
+                thought_signature: None,
             }]),
             ConversationMessage::tool_result(
                 "1",
@@ -697,6 +698,7 @@ mod tests {
                 id: "2".to_string(),
                 name: "edit_file".to_string(),
                 input: r#"{"path":"src/main.rs","old":"old","new":"new"}"#.to_string(),
+                thought_signature: None,
             }]),
             ConversationMessage::tool_result(
                 "2",
@@ -718,6 +720,7 @@ mod tests {
                 id: "1".to_string(),
                 name: "read_file".to_string(),
                 input: r#"{"path":"src/main.rs"}"#.to_string(),
+                thought_signature: None,
             }]),
             ConversationMessage::tool_result(
                 "1",
@@ -746,6 +749,7 @@ mod tests {
                 id: "t".to_string(),
                 name: "bash".to_string(),
                 input: r#"{"command":"ls"}"#.to_string(),
+                thought_signature: None,
             },
         ]));
 
@@ -764,6 +768,7 @@ mod tests {
                     id: format!("read_{i}"),
                     name: "read_file".to_string(),
                     input: format!(r#"{{"path":"src/{i}.rs"}}"#),
+                    thought_signature: None,
                 },
             ]));
             messages.push(ConversationMessage::tool_result(
@@ -789,6 +794,7 @@ mod tests {
                 id: "1".to_string(),
                 name: "read_file".to_string(),
                 input: r#"{"path":"src/main.rs"}"#.to_string(),
+                thought_signature: None,
             }]),
             ConversationMessage::tool_result(
                 "1",
@@ -800,6 +806,7 @@ mod tests {
                 id: "2".to_string(),
                 name: "edit_file".to_string(),
                 input: r#"{"path":"src/main.rs","old":"buggy","new":"fixed"}"#.to_string(),
+                thought_signature: None,
             }]),
             ConversationMessage::tool_result(
                 "2",
diff --git a/rust/crates/rusty-claude-cli/src/main.rs b/rust/crates/rusty-claude-cli/src/main.rs
index a4f14a2e..ad8c8ed9 100644
--- a/rust/crates/rusty-claude-cli/src/main.rs
+++ b/rust/crates/rusty-claude-cli/src/main.rs
@@ -10414,7 +10414,7 @@ fn render_last_tool_debug_report(session: &Session) -> Result<String, Box<dyn st
         .rev()
         .find_map(|message| {
             message.blocks.iter().rev().find_map(|block| match block {
-                ContentBlock::ToolUse { id, name, input } => {
+                ContentBlock::ToolUse { id, name, input, .. } => {
                     Some((id.clone(), name.clone(), input.clone()))
                 }
                 _ => None,
@@ -10751,7 +10751,7 @@ fn render_export_text(session: &Session) -> String {
             match block {
                 ContentBlock::Text { text } => lines.push(text.clone()),
                 ContentBlock::Thinking { .. } => {}
-                ContentBlock::ToolUse { id, name, input } => {
+                ContentBlock::ToolUse { id, name, input, .. } => {
                     lines.push(format!("[tool_use id={id} name={name}] {input}"));
                 }
                 ContentBlock::ToolResult {
@@ -10989,7 +10989,7 @@ fn render_session_markdown(session: &Session, session_id: &str, session_path: &P
                     }
                 }
                 ContentBlock::Thinking { .. } => {}
-                ContentBlock::ToolUse { id, name, input } => {
+                ContentBlock::ToolUse { id, name, input, .. } => {
                     lines.push(format!(
                         "**Tool call** `{name}` _(id `{}`)_",
                         short_tool_id(id)
@@ -11872,7 +11872,7 @@ impl AnthropicRuntimeClient {
         let renderer = TerminalRenderer::new();
         let mut markdown_stream = MarkdownStreamState::default();
         let mut events = Vec::new();
-        let mut pending_tool: Option<(String, String, String)> = None;
+        let mut pending_tool: Option<(String, String, String, Option<String>)> = None;
         // 累积 reasoning_content 到 Thinking 块（修复 DeepSeek V4 reasoning_content 协议 bug）
         let mut pending_thinking: Option<(String, Option<String>)> = None;
         let mut block_has_thinking_summary = false;
@@ -11948,7 +11948,7 @@ impl AnthropicRuntimeClient {
                         }
                     }
                     ContentBlockDelta::InputJsonDelta { partial_json } => {
-                        if let Some((_, _, input)) = &mut pending_tool {
+                        if let Some((_, _, input, _)) = &mut pending_tool {
                             input.push_str(&partial_json);
                         }
                     }
@@ -11983,7 +11983,7 @@ impl AnthropicRuntimeClient {
                             signature,
                         });
                     }
-                    if let Some((id, name, input)) = pending_tool.take() {
+                    if let Some((id, name, input, thought_signature)) = pending_tool.take() {
                         if let Some(progress_reporter) = &self.progress_reporter {
                             progress_reporter.mark_tool_phase(&name, &input);
                         }
@@ -11991,7 +11991,7 @@ impl AnthropicRuntimeClient {
                         writeln!(out, "\n{}", format_tool_call_start(&name, &input))
                             .and_then(|()| out.flush())
                             .map_err(|error| RuntimeError::new(error.to_string()))?;
-                        events.push(AssistantEvent::ToolUse { id, name, input });
+                        events.push(AssistantEvent::ToolUse { id, name, input, thought_signature });
                     }
                 }
                 ApiStreamEvent::MessageDelta(delta) => {
@@ -12167,7 +12167,7 @@ fn collect_tool_uses(summary: &runtime::TurnSummary) -> Vec<serde_json::Value> {
         .iter()
         .flat_map(|message| message.blocks.iter())
         .filter_map(|block| match block {
-            ContentBlock::ToolUse { id, name, input } => Some(json!({
+            ContentBlock::ToolUse { id, name, input, .. } => Some(json!({
                 "id": id,
                 "name": name,
                 "input": input,
@@ -12868,7 +12868,7 @@ fn push_output_block(
     block: OutputContentBlock,
     out: &mut (impl Write + ?Sized),
     events: &mut Vec<AssistantEvent>,
-    pending_tool: &mut Option<(String, String, String)>,
+    pending_tool: &mut Option<(String, String, String, Option<String>)>,
     streaming_tool_input: bool,
     block_has_thinking_summary: &mut bool,
 ) -> Result<(), RuntimeError> {
@@ -12882,7 +12882,7 @@ fn push_output_block(
                 events.push(AssistantEvent::TextDelta(text));
             }
         }
-        OutputContentBlock::ToolUse { id, name, input } => {
+        OutputContentBlock::ToolUse { id, name, input, thought_signature } => {
             // During streaming, the initial content_block_start has an empty input ({}).
             // The real input arrives via input_json_delta events. In
             // non-streaming responses, preserve a legitimate empty object.
@@ -12894,7 +12894,7 @@ fn push_output_block(
             } else {
                 input.to_string()
             };
-            *pending_tool = Some((id, name, initial_input));
+            *pending_tool = Some((id, name, initial_input, thought_signature));
         }
         OutputContentBlock::Thinking { thinking, .. } => {
             render_thinking_block_summary(out, Some(thinking.chars().count()), false)?;
@@ -12925,8 +12925,8 @@ fn response_to_events(
             false,
             &mut block_has_thinking_summary,
         )?;
-        if let Some((id, name, input)) = pending_tool.take() {
-            events.push(AssistantEvent::ToolUse { id, name, input });
+        if let Some((id, name, input, thought_signature)) = pending_tool.take() {
+            events.push(AssistantEvent::ToolUse { id, name, input, thought_signature });
         }
     }
 
@@ -13130,11 +13130,12 @@ fn convert_messages(messages: &[ConversationMessage]) -> Vec<InputMessage> {
                             signature: signature.clone(),
                         })
                     }
-                    ContentBlock::ToolUse { id, name, input } => Some(InputContentBlock::ToolUse {
+                    ContentBlock::ToolUse { id, name, input, thought_signature, .. } => Some(InputContentBlock::ToolUse {
                         id: id.clone(),
                         name: name.clone(),
                         input: serde_json::from_str(input)
                             .unwrap_or_else(|_| serde_json::json!({ "raw": input })),
+                        thought_signature: thought_signature.clone(),
                     }),
                     ContentBlock::ToolResult {
                         tool_use_id,
@@ -15728,6 +15729,7 @@ mod tests {
                     id: "toolu_abcdefghijklmnop".to_string(),
                     name: "bash".to_string(),
                     input: r#"{"command":"ls -la"}"#.to_string(),
+                    thought_signature: None,
                 },
             ]),
             ConversationMessage {
@@ -17669,6 +17671,7 @@ UU conflicted.rs",
                 id: "tool-1".to_string(),
                 name: "bash".to_string(),
                 input: "{\"command\":\"pwd\"}".to_string(),
+                thought_signature: None,
             }]),
             ConversationMessage {
                 role: MessageRole::Tool,
@@ -18059,6 +18062,7 @@ UU conflicted.rs",
                 id: "tool-1".to_string(),
                 name: "read_file".to_string(),
                 input: json!({}),
+                thought_signature: None,
             },
             &mut out,
             &mut events,
@@ -18071,7 +18075,7 @@ UU conflicted.rs",
         assert!(events.is_empty());
         assert_eq!(
             pending_tool,
-            Some(("tool-1".to_string(), "read_file".to_string(), String::new(),))
+            Some(("tool-1".to_string(), "read_file".to_string(), String::new(), None))
         );
     }
 
@@ -18088,6 +18092,7 @@ UU conflicted.rs",
                     id: "tool-1".to_string(),
                     name: "read_file".to_string(),
                     input: json!({}),
+                    thought_signature: None,
                 }],
                 stop_reason: Some("tool_use".to_string()),
                 stop_sequence: None,
@@ -18123,6 +18128,7 @@ UU conflicted.rs",
                     id: "tool-2".to_string(),
                     name: "read_file".to_string(),
                     input: json!({ "path": "rust/Cargo.toml" }),
+                    thought_signature: None,
                 }],
                 stop_reason: Some("tool_use".to_string()),
                 stop_sequence: None,
diff --git a/rust/crates/tools/src/lib.rs b/rust/crates/tools/src/lib.rs
index 15dff721..1089f819 100644
--- a/rust/crates/tools/src/lib.rs
+++ b/rust/crates/tools/src/lib.rs
@@ -5203,7 +5203,7 @@ async fn stream_with_provider(
 ) -> Result<Vec<AssistantEvent>, ApiError> {
     let mut stream = client.stream_message(message_request).await?;
     let mut events = Vec::new();
-    let mut pending_tools: BTreeMap<u32, (String, String, String)> = BTreeMap::new();
+    let mut pending_tools: BTreeMap<u32, (String, String, String, Option<String>)> = BTreeMap::new();
     let mut pending_thinking: BTreeMap<u32, (String, Option<String>)> = BTreeMap::new();
     let mut saw_stop = false;
 
@@ -5238,7 +5238,7 @@ async fn stream_with_provider(
                     }
                 }
                 ContentBlockDelta::InputJsonDelta { partial_json } => {
-                    if let Some((_, _, input)) = pending_tools.get_mut(&delta.index) {
+                    if let Some((_, _, input, _)) = pending_tools.get_mut(&delta.index) {
                         input.push_str(&partial_json);
                     }
                 }
@@ -5262,8 +5262,8 @@ async fn stream_with_provider(
                         signature,
                     });
                 }
-                if let Some((id, name, input)) = pending_tools.remove(&stop.index) {
-                    events.push(AssistantEvent::ToolUse { id, name, input });
+                if let Some((id, name, input, thought_signature)) = pending_tools.remove(&stop.index) {
+                    events.push(AssistantEvent::ToolUse { id, name, input, thought_signature });
                 }
             }
             ApiStreamEvent::MessageDelta(delta) => {
@@ -5371,11 +5371,12 @@ fn convert_messages(messages: &[ConversationMessage]) -> Vec<InputMessage> {
                         thinking: thinking.clone(),
                         signature: signature.clone(),
                     },
-                    ContentBlock::ToolUse { id, name, input } => InputContentBlock::ToolUse {
+                    ContentBlock::ToolUse { id, name, input, thought_signature } => InputContentBlock::ToolUse {
                         id: id.clone(),
                         name: name.clone(),
                         input: serde_json::from_str(input)
                             .unwrap_or_else(|_| serde_json::json!({ "raw": input })),
+                        thought_signature: thought_signature.clone(),
                     },
                     ContentBlock::ToolResult {
                         tool_use_id,
@@ -5406,7 +5407,7 @@ fn push_output_block(
     block: OutputContentBlock,
     block_index: u32,
     events: &mut Vec<AssistantEvent>,
-    pending_tools: &mut BTreeMap<u32, (String, String, String)>,
+    pending_tools: &mut BTreeMap<u32, (String, String, String, Option<String>)>,
     pending_thinking: &mut BTreeMap<u32, (String, Option<String>)>,
     streaming_tool_input: bool,
 ) {
@@ -5416,7 +5417,7 @@ fn push_output_block(
                 events.push(AssistantEvent::TextDelta(text));
             }
         }
-        OutputContentBlock::ToolUse { id, name, input } => {
+        OutputContentBlock::ToolUse { id, name, input, thought_signature } => {
             let initial_input = if streaming_tool_input
                 && input.is_object()
                 && input.as_object().is_some_and(serde_json::Map::is_empty)
@@ -5425,7 +5426,7 @@ fn push_output_block(
             } else {
                 input.to_string()
             };
-            pending_tools.insert(block_index, (id, name, initial_input));
+            pending_tools.insert(block_index, (id, name, initial_input, thought_signature));
         }
         OutputContentBlock::Thinking {
             thinking,
@@ -5459,8 +5460,8 @@ fn response_to_events(response: MessageResponse) -> Vec<AssistantEvent> {
             &mut pending_thinking,
             false,
         );
-        if let Some((id, name, input)) = pending_tools.remove(&index) {
-            events.push(AssistantEvent::ToolUse { id, name, input });
+        if let Some((id, name, input, thought_signature)) = pending_tools.remove(&index) {
+            events.push(AssistantEvent::ToolUse { id, name, input, thought_signature });
         }
     }
 
@@ -8066,6 +8067,7 @@ mod tests {
                 id: "tool-1".to_string(),
                 name: "read_file".to_string(),
                 input: json!({}),
+                thought_signature: None,
             },
             1,
             &mut events,
@@ -8078,6 +8080,7 @@ mod tests {
                 id: "tool-2".to_string(),
                 name: "grep_search".to_string(),
                 input: json!({}),
+                thought_signature: None,
             },
             2,
             &mut events,
@@ -9358,6 +9361,7 @@ mod tests {
                             id: "tool-1".to_string(),
                             name: "read_file".to_string(),
                             input: json!({ "path": self.input_path }).to_string(),
+                            thought_signature: None,
                         },
                         AssistantEvent::MessageStop,
                     ])