Submission queue

multitaskStrategy: "enqueue" lets the user fire additional submits while another run is in flight. The queue is fully client-side — entries drain sequentially as the active run terminates — and is observable through the useSubmissionQueue companion hook.

Learn more: For queued-input UX, see the message queues documentation.

Multitask strategies

Pass multitaskStrategy to submit() to control what happens when a submit lands while a run is already active:

Strategy	Behaviour
"rollback"	Default. Aborts the active run and immediately dispatches the new one.
"reject"	Drops the new submit. The returned promise rejects.
"enqueue"	Appends the submit to the client-side queue. Entries drain sequentially once the active run terminates.
"interrupt"	Currently falls back to "rollback" semantics client-side, pending server-side support.

Enqueueing runs

import { HumanMessage } from "@langchain/core/messages";

void stream.submit({ messages: [new HumanMessage("follow-up")] }, { multitaskStrategy: "enqueue" });

Nothing special happens on the return value — the promise resolves when the enqueued run eventually completes. You can fire several in a row; they dispatch in call order.

useSubmissionQueue

Subscribe to the queue reactively from any component:

import { useStream, useSubmissionQueue, type AnyStream } from "@langchain/svelte";
import { HumanMessage } from "@langchain/core/messages";

function Composer({ stream }: { stream: AnyStream }) {
  const { entries, size, cancel, clear } = useSubmissionQueue(stream);

  return (
    <>
      <button
        onClick={() =>
          stream.submit({ messages: [new HumanMessage("go")] }, { multitaskStrategy: "enqueue" })
        }
      >
        Queue turn
      </button>

      {size > 0 && (
        <div>
          <p>{size} queued</p>
          <ol>
            {entries.map((e) => (
              <li key={e.id}>
                pending… <button onClick={() => cancel(e.id)}>cancel</button>
              </li>
            ))}
          </ol>
          <button onClick={clear}>Clear queue</button>
        </div>
      )}
    </>
  );
}

Return shape

Field	Type	Description
entries	readonly SubmissionQueueEntry[]	All pending entries, in dispatch order.
size	number	Alias for entries.length.
cancel(id)	(id: string) => Promise<boolean>	Removes one entry by id; resolves true on hit.
clear()	() => Promise<void>	Empties the queue.

Each SubmissionQueueEntry carries { id, input, options, enqueuedAt } so you can render the queued input ahead of its dispatch.

Cancelling, clearing, and thread switches

• cancel(id) removes a single entry. The run is never dispatched.
• clear() empties the queue but does not affect the active run. Pair with stream.stop() if you also need to abort the in-flight work.
• Switching threadId clears the queue — entries were targeted at the previous thread, so dispatching them against the new one would be surprising.

API reference