diff --git a/src/providers/gemini.rs b/src/providers/gemini.rs
index 5db27d8c..a2f1f78e 100644
--- a/src/providers/gemini.rs
+++ b/src/providers/gemini.rs
@@ -57,8 +57,6 @@ struct GeminiPart {
     function_response: Option<GeminiFunctionResponse>,
     #[serde(skip_serializing_if = "Option::is_none")]
     thought: Option<String>,
-    #[serde(skip_serializing_if = "Option::is_none")]
-    thought_signature: Option<String>,
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
@@ -72,6 +70,8 @@ struct GeminiInlineData {
 struct GeminiFunctionCall {
     name: String,
     args: Value,
+    #[serde(skip_serializing_if = "Option::is_none", rename = "thought_signature")]
+    thought_signature: Option<String>,
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
@@ -231,7 +231,6 @@ impl GeminiProvider {
                                 function_call: None,
                                 function_response: None,
                                 thought: None,
-                                thought_signature: None,
                             });
                         }
                     }
@@ -271,7 +270,6 @@ impl GeminiProvider {
                         response: response_value,
                     }),
                     thought: None,
-                    thought_signature: None,
                 });
             } else if msg.role == "assistant" {
                 // Assistant messages: handle text, thought (reasoning), and tool_calls
@@ -284,7 +282,6 @@ impl GeminiProvider {
                                 function_call: None,
                                 function_response: None,
                                 thought: None,
-                                thought_signature: None,
                             });
                         }
                     }
@@ -299,7 +296,6 @@ impl GeminiProvider {
                             function_call: None,
                             function_response: None,
                             thought: Some(reasoning.clone()),
-                            thought_signature: None,
                         });
                     }
                 }
@@ -324,10 +320,10 @@ impl GeminiProvider {
                             function_call: Some(GeminiFunctionCall {
                                 name: tc.function.name.clone(),
                                 args,
+                                thought_signature,
                             }),
                             function_response: None,
                             thought: None,
-                            thought_signature,
                         });
                     }
                 }
@@ -343,7 +339,6 @@ impl GeminiProvider {
                                     function_call: None,
                                     function_response: None,
                                     thought: None,
-                                    thought_signature: None,
                                 });
                             }
                         }
@@ -362,7 +357,6 @@ impl GeminiProvider {
                                 function_call: None,
                                 function_response: None,
                                 thought: None,
-                                thought_signature: None,
                             });
                         }
                     }
@@ -398,7 +392,6 @@ impl GeminiProvider {
                         function_call: None,
                         function_response: None,
                         thought: None,
-                        thought_signature: None,
                     }],
                 });
             }
@@ -525,11 +518,10 @@ impl GeminiProvider {
     fn extract_tool_calls(parts: &[GeminiPart]) -> Option<Vec<ToolCall>> {
         let calls: Vec<ToolCall> = parts
             .iter()
-            .filter(|p| p.function_call.is_some())
-            .map(|p| {
-                let fc = p.function_call.as_ref().unwrap();
-                // CAPTURE: Use thought_signature from Part as the ID if available
-                let id = p.thought_signature.clone().unwrap_or_else(|| format!("call_{}", Uuid::new_v4().simple()));
+            .filter_map(|p| p.function_call.as_ref())
+            .map(|fc| {
+                // CAPTURE: Use thought_signature from functionCall as the ID if available
+                let id = fc.thought_signature.clone().unwrap_or_else(|| format!("call_{}", Uuid::new_v4().simple()));
                 
                 ToolCall {
                     id,
@@ -549,12 +541,11 @@ impl GeminiProvider {
     fn extract_tool_call_deltas(parts: &[GeminiPart]) -> Option<Vec<ToolCallDelta>> {
         let deltas: Vec<ToolCallDelta> = parts
             .iter()
+            .filter_map(|p| p.function_call.as_ref())
             .enumerate()
-            .filter(|(_, p)| p.function_call.is_some())
-            .map(|(i, p)| {
-                let fc = p.function_call.as_ref().unwrap();
-                // CAPTURE: Use thought_signature from Part as the ID if available
-                let id = p.thought_signature.clone().unwrap_or_else(|| format!("call_{}", Uuid::new_v4().simple()));
+            .map(|(i, fc)| {
+                // CAPTURE: Use thought_signature from functionCall as the ID if available
+                let id = fc.thought_signature.clone().unwrap_or_else(|| format!("call_{}", Uuid::new_v4().simple()));
 
                 ToolCallDelta {
                     index: i as u32,