Yes—doable. In Prefect 3.x, the way to “fire-and-forget” a child flow is to trigger its deployment and not wait for completion. Key points: - Calling a flow function directly (e.g.,

child_flow()

) will wait for it to finish. - Use

run_deployment(..., timeout=0)

to return immediately after the child run is scheduled. - Keep it linked as a “subflow” in the UI with

as_subflow=True

(default), or make it totally independent with

as_subflow=False

. Examples - Async parent flow (continues immediately, child stays linked as subflow):

from prefect import flow
from prefect.deployments import run_deployment

@flow
async def parent():
    child_run = await run_deployment(
        name="child_flow/child_deployment",
        parameters={"x": 1},
        timeout=0,       # don't wait
        as_subflow=True  # keep parent/child link (default)
    )
    print(f"Started child run {child_run.id}")
    # parent continues immediately

- Sync parent flow (also returns immediately; set as_subflow to False to make it independent):

from prefect import flow
from prefect.deployments import run_deployment

@flow
def parent():
    child_run = run_deployment(
        name="child_flow/child_deployment",
        parameters={"x": 1},
        timeout=0,
        as_subflow=False  # set False if you want no parent-child link
    )
    print(f"Started child run {child_run.id}")
    # parent continues immediately

- If you prefer using the client directly:

from prefect import flow, get_client

@flow
async def parent():
    async with get_client() as client:
        fr = await client.create_flow_run_from_deployment(
            deployment_id="YOUR-DEPLOYMENT-ID",
            parameters={"x": 1},
            # parent_task_run_id set automatically if you want it as a subflow;
            # set None for independence
        )
    # parent continues immediately

Notes - You must have a deployment for the child flow and a worker picking up its work. - If by “subflow” you mean calling

child_flow()

directly, that will always wait—use a deployment trigger instead to avoid blocking. Would you like me to show how to create the child deployment, or are you already set up with one?