diff --git a/server/utils/agents/aibitat/providers/gemini.js b/server/utils/agents/aibitat/providers/gemini.js
index 53d3113a..9b43d49f 100644
--- a/server/utils/agents/aibitat/providers/gemini.js
+++ b/server/utils/agents/aibitat/providers/gemini.js
@@ -83,6 +83,10 @@ class GeminiProvider extends Provider {
    * Format the messages to the Gemini API Responses format.
    * - Gemini has some loosely documented format for tool calls and it can change at any time.
    * - We need to map the function call to the correct id and Gemini will throw an error if it does not.
+   * - Gemini requires a `thought_signature` (via `extra_content.google.thought_signature`) on function call
+   *   parts in multi-turn tool conversations. This is an encrypted token Gemini attaches to every tool call
+   *   it makes, and it must be passed back when sending tool results or Gemini rejects the request with a 400.
+   *   See: https://ai.google.dev/gemini-api/docs/thought-signatures
    * @param {any[]} messages - The messages to format.
    * @returns {OpenAI.OpenAI.Responses.ResponseInput[]} The formatted messages.
    */
@@ -101,17 +105,25 @@ class GeminiProvider extends Provider {
           return;
         }
 
+        const prefixedName = this.prefixToolCall(
+          message.originalFunctionCall.name,
+          "add"
+        );
         formattedMessages.push(
           {
             role: "assistant",
+            content: "",
             tool_calls: [
               {
                 type: "function",
+                ...(message.originalFunctionCall.extra_content
+                  ? { extra_content: message.originalFunctionCall.extra_content }
+                  : {}),
                 function: {
                   arguments: JSON.stringify(
                     message.originalFunctionCall.arguments
                   ),
-                  name: message.originalFunctionCall.name,
+                  name: prefixedName,
                 },
                 id: message.originalFunctionCall.id,
               },
@@ -120,6 +132,7 @@ class GeminiProvider extends Provider {
           {
             role: "tool",
             tool_call_id: message.originalFunctionCall.id,
+            name: prefixedName,
             content: message.content,
           }
         );
@@ -188,6 +201,8 @@ class GeminiProvider extends Provider {
             name: this.prefixToolCall(toolCall.function.name, "strip"),
             call_id: toolCall.id,
             arguments: toolCall.function.arguments,
+            // Preserve Gemini's thought_signature so it can be passed back in #formatMessages
+            extra_content: toolCall.extra_content ?? null,
           };
           eventHandler?.("reportStreamEvent", {
             type: "toolCallInvocation",
@@ -208,6 +223,7 @@ class GeminiProvider extends Provider {
             id: completion.functionCall.call_id,
             name: completion.functionCall.name,
             arguments: completion.functionCall.arguments,
+            extra_content: completion.functionCall.extra_content,
           },
           cost: this.getCost(),
         };
@@ -265,6 +281,8 @@ class GeminiProvider extends Provider {
             name: this.prefixToolCall(toolCall.function.name, "strip"),
             arguments: functionArgs,
             id: toolCall.id,
+            // Preserve Gemini's thought_signature so it can be passed back in #formatMessages
+            extra_content: toolCall.extra_content ?? null,
           },
           cost,
         };