diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5a73a9d..e3b468c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,9 @@
 - **Public File URLs**: Added `client.files.create_public_url()` and `client.files.revoke_public_url()` (sync and async) to create and revoke publicly shareable, unauthenticated URLs for stored files. `create_public_url()` accepts an optional `expires_after` (an `int` in seconds or a `datetime.timedelta`).
 - **Files List Filter**: `client.files.list()` (sync and async) now accepts an optional `filter` parameter to narrow results server-side by fields such as `content_type`, `size_bytes`, `created_at`, `upload_status`, and `public_url` (e.g. `filter='public_url != null'`).
 
+### Fixed
+- `chat.append(response)` now sets `tool_call_id` on replayed tool-role messages (recovered from the tool call echoed on the output), so servers can pair replayed tool turns with their originating calls. This fixes stateless multi-turn follow-ups to server-side tools whose results are re-hydrated by ID — e.g. editing a previously generated image in-memory without `previous_response_id`.
+
 ## [v1.14.0]
 ### Added
 - **Image Search**: Added `enable_image_search` parameter to `web_search()` to return image results that can be embedded in responses
diff --git a/src/xai_sdk/chat.py b/src/xai_sdk/chat.py
index 9c47977..c6386b9 100644
--- a/src/xai_sdk/chat.py
+++ b/src/xai_sdk/chat.py
@@ -267,6 +267,20 @@ def _make_chat(self, conversation_id: Optional[str], batch_request_id: Optional[
         """Creates the proto wrapper for chat requests."""
 
 
+def _replay_tool_call_id(output_message: chat_pb2.CompletionMessage) -> Optional[str]:
+    """Recovers the `tool_call_id` for replaying a completion output as an input message.
+
+    `chat_pb2.CompletionMessage` does not carry a `tool_call_id` field, but server-side
+    tool outputs (ROLE_TOOL) echo the originating call in `tool_calls`. The server pairs
+    replayed tool turns with their calls via `Message.tool_call_id` (e.g. to re-hydrate
+    binary tool results such as generated images), so it must be set when appending a
+    response back onto the conversation.
+    """
+    if output_message.role == chat_pb2.MessageRole.ROLE_TOOL and output_message.tool_calls:
+        return output_message.tool_calls[0].id
+    return None
+
+
 class BaseChat(ProtoDecorator[chat_pb2.GetCompletionsRequest]):
     """Utility class for simplifying the interaction with Chat requests and responses."""
 
@@ -377,16 +391,19 @@ def append(self, message: Union[chat_pb2.Message, "Response", "CompactContextRes
                             reasoning_content=output.message.reasoning_content,
                             encrypted_content=output.message.encrypted_content,
                             tool_calls=output.message.tool_calls,
+                            tool_call_id=_replay_tool_call_id(output.message),
                         )
                     )
             else:
+                output_message = message._get_output().message
                 self._proto.messages.append(
                     chat_pb2.Message(
-                        role=message._get_output().message.role,
+                        role=output_message.role,
                         content=[text(message.content)],
                         reasoning_content=message.reasoning_content,
                         encrypted_content=message.encrypted_content,
                         tool_calls=message.tool_calls,
+                        tool_call_id=_replay_tool_call_id(output_message),
                     )
                 )
         else:
diff --git a/tests/chat_test.py b/tests/chat_test.py
index d5c0cb1..c37043e 100644
--- a/tests/chat_test.py
+++ b/tests/chat_test.py
@@ -792,6 +792,82 @@ def test_compact_context_response_empty_encrypted_content():
     assert response.encrypted_content == ""
 
 
+def test_append_agentic_response_sets_tool_call_id_on_tool_messages():
+    """Test that append(Response) links replayed ROLE_TOOL outputs to their originating tool call.
+
+    Server-side hydration pairs replayed tool turns via `Message.tool_call_id` (e.g. to
+    re-hydrate binary results like generated images), so appending an agentic response
+    must set it from the tool call echoed on the ROLE_TOOL output.
+    """
+    from xai_sdk.proto import chat_pb2_grpc
+    from xai_sdk.sync.chat import Chat as SyncChat
+
+    tool_call = chat_pb2.ToolCall(
+        id="call_1",
+        type=chat_pb2.TOOL_CALL_TYPE_WEB_SEARCH_TOOL,
+        status=chat_pb2.TOOL_CALL_STATUS_COMPLETED,
+        function=chat_pb2.FunctionCall(name="web_search", arguments="{}"),
+    )
+    response_pb = chat_pb2.GetChatCompletionResponse(
+        outputs=[
+            chat_pb2.CompletionOutput(
+                index=0,
+                message=chat_pb2.CompletionMessage(role=chat_pb2.MessageRole.ROLE_ASSISTANT, tool_calls=[tool_call]),
+            ),
+            chat_pb2.CompletionOutput(
+                index=1,
+                message=chat_pb2.CompletionMessage(
+                    role=chat_pb2.MessageRole.ROLE_TOOL,
+                    content='{"__type": "web_search_result"}',
+                    tool_calls=[tool_call],
+                ),
+            ),
+            chat_pb2.CompletionOutput(
+                index=2,
+                message=chat_pb2.CompletionMessage(role=chat_pb2.MessageRole.ROLE_ASSISTANT, content="Done!"),
+            ),
+        ]
+    )
+    response = Response(response_pb, None)  # None means agentic: replay all outputs.
+
+    stub = chat_pb2_grpc.ChatStub.__new__(chat_pb2_grpc.ChatStub)
+    chat = SyncChat(stub, None, None, model="grok-4.3")
+    chat.append(response)
+
+    assert len(chat.messages) == 3
+    assert chat.messages[0].role == chat_pb2.MessageRole.ROLE_ASSISTANT
+    assert chat.messages[0].tool_call_id == ""
+    assert chat.messages[1].role == chat_pb2.MessageRole.ROLE_TOOL
+    assert chat.messages[1].tool_call_id == "call_1"
+    assert [tc.id for tc in chat.messages[1].tool_calls] == ["call_1"]
+    assert chat.messages[2].role == chat_pb2.MessageRole.ROLE_ASSISTANT
+    assert chat.messages[2].tool_call_id == ""
+
+
+def test_append_indexed_response_leaves_tool_call_id_unset_on_assistant_message():
+    """Test that append(Response) with an index keeps assistant messages without a tool_call_id."""
+    from xai_sdk.proto import chat_pb2_grpc
+    from xai_sdk.sync.chat import Chat as SyncChat
+
+    response_pb = chat_pb2.GetChatCompletionResponse(
+        outputs=[
+            chat_pb2.CompletionOutput(
+                index=0,
+                message=chat_pb2.CompletionMessage(role=chat_pb2.MessageRole.ROLE_ASSISTANT, content="Hello"),
+            )
+        ]
+    )
+    response = Response(response_pb, 0)
+
+    stub = chat_pb2_grpc.ChatStub.__new__(chat_pb2_grpc.ChatStub)
+    chat = SyncChat(stub, None, None, model="grok-4.3")
+    chat.append(response)
+
+    assert len(chat.messages) == 1
+    assert chat.messages[0].role == chat_pb2.MessageRole.ROLE_ASSISTANT
+    assert chat.messages[0].tool_call_id == ""
+
+
 def test_append_compact_context_response_creates_user_message():
     """Test that append(CompactContextResponse) produces a ROLE_USER message with encrypted_content."""
     from xai_sdk.proto import chat_pb2_grpc