Background runs on one session now execute one at a time, in the order you sent them

With QueueConfig(durable=True), Agno's AgentOS stamps every background ticket with a session_seq, and a worker claims it only once no earlier run in the same session is still queued, running or paused. The rule covers agents, teams and workflows alike.

Picture a chat client that lets someone send a second message before the first answer arrives. Earlier releases ran both turns side by side: the second loaded its history before the first had written anything, session state went to whichever run saved last, and answers could land out of order.

A waiting run stays queued and spends no attempt and no worker slot. Runs on other sessions keep executing concurrently, up to max_concurrency. A run paused for human approval holds its session until someone continues or cancels it, since the runs behind it probably depend on its outcome, and a continued or retried run keeps its place in line.

We submitted three background runs to one session and one to another on an embedded Postgres, with a stub model that waits one second standing in for a real one.

The setting is on by default:

from agno.os import AgentOS, QueueConfig
 
agent_os = AgentOS(
    agents=[agent],
    db=db,
    queue=QueueConfig(durable=True),  # queue_per_session=True is the default
)

GET /config reports what the queue actually enforces, so a client can discover it without admin access:

GET /config queue: {"durable": true, "queue_per_session": true}

Pass queue_per_session=False to let runs on one session execute concurrently again. Claude, Codex and the other external agents stay serialized either way, because their sessions refuse a second concurrent turn. A custom queue store opts in by setting serializes_sessions = True; without it, the worker logs that marked tickets run concurrently and /config reports queue_per_session: false.

The line only covers runs that go through the durable queue. Media uploads, non-JSON payloads and direct non-background calls run outside it, so keep them off sessions that also take queued runs.

See the cookbook, and learn more about the durable queue in the documentation.