Easiest: use the runtime helper in Prefect 3.x.

from prefect import flow
from prefect.runtime import flow_run

@flow
def child_flow():
    parent_id = flow_run.parent_flow_run_id  # None if this is a root flow
    print(f"Parent flow run ID: {parent_id}")
    return parent_id

Notes: -

flow_run.parent_flow_run_id

returns the calling flow’s run ID when you’re in a subflow, otherwise

None

. - Related helpers you may find useful:

flow_run.id

(current flow run),

flow_run.root_flow_run_id

(top-level flow in the chain). If you need to fetch details about the parent run:

from prefect import flow
from prefect.runtime import flow_run
from prefect.client.orchestration import get_client

@flow
async def child_flow():
    parent_id = flow_run.parent_flow_run_id
    if parent_id:
        async with get_client() as client:
            parent = await client.read_flow_run(parent_id)
            print(f"Parent flow name: {parent.name}")
    return parent_id