diff --git a/libs/sdk-js/src/client.ts b/libs/sdk-js/src/client.ts
index ecf7147ca..14284bcff 100644
--- a/libs/sdk-js/src/client.ts
+++ b/libs/sdk-js/src/client.ts
@@ -1021,19 +1021,28 @@ export class RunsClient extends BaseClient {
    *
    * @param threadId The ID of the thread.
    * @param runId The ID of the run.
-   * @param signal An optional abort signal.
    * @returns An async generator yielding stream parts.
    */
   async *joinStream(
     threadId: string,
     runId: string,
-    signal?: AbortSignal,
+    options?:
+      | { signal?: AbortSignal; cancelOnDisconnect?: boolean }
+      | AbortSignal,
   ): AsyncGenerator<{ event: StreamEvent; data: any }> {
+    const opts =
+      typeof options === "object" &&
+      options != null &&
+      options instanceof AbortSignal
+        ? { signal: options }
+        : options;
+
     const response = await this.asyncCaller.fetch(
       ...this.prepareFetchOptions(`/threads/${threadId}/runs/${runId}/stream`, {
         method: "GET",
         timeoutMs: null,
-        signal,
+        signal: opts?.signal,
+        params: { cancel_on_disconnect: opts?.cancelOnDisconnect ? "1" : "0" },
       }),
     );
 
@@ -1048,7 +1057,7 @@ export class RunsClient extends BaseClient {
         async start(ctrl) {
           parser = createParser((event) => {
             if (
-              (signal && signal.aborted) ||
+              (opts?.signal && opts.signal.aborted) ||
               (event.type === "event" && event.data === "[DONE]")
             ) {
               ctrl.terminate();
diff --git a/libs/sdk-py/langgraph_sdk/client.py b/libs/sdk-py/langgraph_sdk/client.py
index b7cc1a78c..7a959a477 100644
--- a/libs/sdk-py/langgraph_sdk/client.py
+++ b/libs/sdk-py/langgraph_sdk/client.py
@@ -1796,7 +1796,9 @@ class RunsClient:
         """  # noqa: E501
         return await self.http.get(f"/threads/{thread_id}/runs/{run_id}/join")
 
-    def join_stream(self, thread_id: str, run_id: str) -> AsyncIterator[StreamPart]:
+    def join_stream(
+        self, thread_id: str, run_id: str, *, cancel_on_disconnect: bool = False
+    ) -> AsyncIterator[StreamPart]:
         """Stream output from a run in real-time, until the run is done.
         Output is not buffered, so any output produced before this call will
         not be received here.
@@ -1804,6 +1806,7 @@ class RunsClient:
         Args:
             thread_id: The thread ID to join.
             run_id: The run ID to join.
+            cancel_on_disconnect: Whether to cancel the run when the stream is disconnected.
 
         Returns:
             None
@@ -1816,7 +1819,11 @@ class RunsClient:
             )
 
         """  # noqa: E501
-        return self.http.stream(f"/threads/{thread_id}/runs/{run_id}/stream", "GET")
+        return self.http.stream(
+            f"/threads/{thread_id}/runs/{run_id}/stream",
+            "GET",
+            params={"cancel_on_disconnect": cancel_on_disconnect},
+        )
 
     async def delete(self, thread_id: str, run_id: str) -> None:
         """Delete a run.