In Prefect 3.x, you can read the root (top-level) flow’s run ID from any subflow using the runtime context. - In flow C,

prefect.runtime.flow_run.root_flow_run_id

gives you A’s run ID -

prefect.runtime.flow_run.parent_flow_run_id

gives you B’s run ID -

prefect.runtime.flow_run.id

gives you C’s run ID Note: these are attributes, not function calls (no parentheses). Example:

from prefect import flow
from prefect.runtime import flow_run

@flow
def flow_c():
    print(f"C run id: {flow_run.id}")
    print(f"B (parent) run id: {flow_run.parent_flow_run_id}")
    print(f"A (root) run id: {flow_run.root_flow_run_id}")

@flow
def flow_b():
    return flow_c()

@flow
def flow_a():
    return flow_b()

if __name__ == "__main__":
    flow_a()

Alternative (low-level) via context if you prefer UUID objects:

from prefect.context import FlowRunContext

ctx = FlowRunContext.get()
a_run_id = str(ctx.flow_run.root_flow_run_id)  # UUID -> string

If you want links to docs, see: - Runtime flow run attributes: prefect.runtime.flow_run