diff --git a/letta/adapters/letta_llm_request_adapter.py b/letta/adapters/letta_llm_request_adapter.py
index 17c3a77f..8ea95680 100644
--- a/letta/adapters/letta_llm_request_adapter.py
+++ b/letta/adapters/letta_llm_request_adapter.py
@@ -66,7 +66,13 @@ class LettaLLMRequestAdapter(LettaLLMAdapter):
             self.reasoning_content = [OmittedReasoningContent()]
         elif self.chat_completions_response.choices[0].message.content:
             # Reasoning placed into content for legacy reasons
-            self.reasoning_content = [TextContent(text=self.chat_completions_response.choices[0].message.content)]
+            # Carry thought_signature on TextContent when ReasoningContent doesn't exist to hold it
+            self.reasoning_content = [
+                TextContent(
+                    text=self.chat_completions_response.choices[0].message.content,
+                    signature=self.chat_completions_response.choices[0].message.reasoning_content_signature,
+                )
+            ]
         else:
             # logger.info("No reasoning content found.")
             self.reasoning_content = None
diff --git a/letta/adapters/simple_llm_request_adapter.py b/letta/adapters/simple_llm_request_adapter.py
index 7cf5b260..7cec9472 100644
--- a/letta/adapters/simple_llm_request_adapter.py
+++ b/letta/adapters/simple_llm_request_adapter.py
@@ -81,7 +81,12 @@ class SimpleLLMRequestAdapter(LettaLLMRequestAdapter):
         if self.chat_completions_response.choices[0].message.content:
             # NOTE: big difference - 'content' goes into 'content'
             # Reasoning placed into content for legacy reasons
-            self.content = [TextContent(text=self.chat_completions_response.choices[0].message.content)]
+            # Carry thought_signature on TextContent when ReasoningContent doesn't exist to hold it
+            # (e.g. Gemini 2.5 Flash with include_thoughts=False still returns thought_signature)
+            orphan_sig = (
+                self.chat_completions_response.choices[0].message.reasoning_content_signature if not self.reasoning_content else None
+            )
+            self.content = [TextContent(text=self.chat_completions_response.choices[0].message.content, signature=orphan_sig)]
         else:
             self.content = None
 
diff --git a/letta/agents/letta_agent.py b/letta/agents/letta_agent.py
index 246f6d3f..98e56205 100644
--- a/letta/agents/letta_agent.py
+++ b/letta/agents/letta_agent.py
@@ -370,8 +370,12 @@ class LettaAgent(BaseAgent):
                     elif response.choices[0].message.omitted_reasoning_content:
                         reasoning = [OmittedReasoningContent()]
                     elif response.choices[0].message.content:
+                        # Carry thought_signature on TextContent when ReasoningContent doesn't exist to hold it
                         reasoning = [
-                            TextContent(text=response.choices[0].message.content)
+                            TextContent(
+                                text=response.choices[0].message.content,
+                                signature=response.choices[0].message.reasoning_content_signature,
+                            )
                         ]  # reasoning placed into content for legacy reasons
                     else:
                         self.logger.info("No reasoning content found.")
@@ -703,8 +707,12 @@ class LettaAgent(BaseAgent):
                             )
                         ]
                     elif response.choices[0].message.content:
+                        # Carry thought_signature on TextContent when ReasoningContent doesn't exist to hold it
                         reasoning = [
-                            TextContent(text=response.choices[0].message.content)
+                            TextContent(
+                                text=response.choices[0].message.content,
+                                signature=response.choices[0].message.reasoning_content_signature,
+                            )
                         ]  # reasoning placed into content for legacy reasons
                     elif response.choices[0].message.omitted_reasoning_content:
                         reasoning = [OmittedReasoningContent()]
diff --git a/letta/llm_api/google_vertex_client.py b/letta/llm_api/google_vertex_client.py
index 56ed0ae1..ccbee0ca 100644
--- a/letta/llm_api/google_vertex_client.py
+++ b/letta/llm_api/google_vertex_client.py
@@ -593,6 +593,9 @@ class GoogleVertexClient(LLMClientBase):
                                 content=inner_thoughts,
                                 tool_calls=[tool_call],
                             )
+                            if response_message.thought_signature:
+                                thought_signature = base64.b64encode(response_message.thought_signature).decode("utf-8")
+                                openai_response_message.reasoning_content_signature = thought_signature
                         else:
                             openai_response_message.content = inner_thoughts
                             if openai_response_message.tool_calls is None: