Implementation:PrefectHQ Prefect Pause Flow Run

Metadata
Sources	Prefect
Domains	Orchestration, Human_In_The_Loop
Last Updated	2026-02-09 00:00 GMT

Overview

Concrete function for pausing flow execution and collecting typed human input via UI forms provided by the Prefect library.

Description

The pause_flow_run function suspends a running flow and waits for input from a human via the Prefect UI. It accepts a RunInput subclass that defines the form fields, and returns the populated input when a human submits the form. Supports timeout configuration and initial data for pre-populating the form.

Code Reference

• Repository: https://github.com/PrefectHQ/prefect
• File: src/prefect/flow_runs.py (L334) for pause_flow_run, examples/ai_database_cleanup_with_approval.py (L96-108) for usage
• Signature:

def pause_flow_run(
    wait_for_input: Optional[Type[RunInput]] = None,
    timeout: int = 3600,
) -> RunInput:
    """Pause the current flow run and wait for human input.

    Args:
        wait_for_input: RunInput subclass defining the form.
        timeout: Seconds to wait before timing out.
    Returns:
        Populated RunInput instance with human-provided values.
    """

• Import: from prefect.flow_runs import pause_flow_run; from prefect.input import RunInput

I/O Contract

Inputs

• wait_for_input (Type[RunInput], optional) — form class defining the input fields
• timeout (int, optional) — wait timeout in seconds, default 3600

Outputs

• RunInput instance with populated form fields

Usage Example

from pydantic import Field
from prefect import flow
from prefect.flow_runs import pause_flow_run
from prefect.input import RunInput

class CleanupApproval(RunInput):
    approve: bool = Field(default=False)
    notes: str = Field(default="", description="Why approve/reject?")

@flow(name="human-approval")
def get_human_approval(preview: str, count: int) -> tuple[bool, str]:
    approval = pause_flow_run(
        wait_for_input=CleanupApproval.with_initial_data(
            description=f"**Preview ({count} runs):**\n{preview}"
        ),
        timeout=3600,
    )
    return approval.approve, approval.notes

Related Pages

• Principle:PrefectHQ_Prefect_Human_Approval_Gate