Short answer: that setting doesn’t exist in Prefect 2.x. It’s a Prefect 3.x setting, so 2.x warns “Unknown setting.” What to do in 2.x: - Remove/unset

PREFECT_SERVER_ALLOW_EPHEMERAL_MODE

from your environment or

prefect.toml

. - Bash:

unset PREFECT_SERVER_ALLOW_EPHEMERAL_MODE

- Then restart your shell/process. - Point Prefect 2.x at a real API instead: - Prefect Cloud: log in and let it set

PREFECT_API_URL

prefect cloud login

- Local Orion (2.x): run the local server and set

PREFECT_API_URL

to it (default is `http://127.0.0.1:4200/api`).

export PREFECT_API_URL="<http://127.0.0.1:4200/api>"

Then start your local Orion server (in 2.x this is typically

prefect orion start

). Why this happens: -

PREFECT_SERVER_ALLOW_EPHEMERAL_MODE

is a Prefect 3.x toggle for “ephemeral” server behavior. It’s not recognized by the 2.x config system, hence the error. Example of it in 3.x context: prefecthq/prefect#15818. If you actually meant to use Prefect 3.x, keep the setting and set

PREFECT_SERVER_ALLOW_EPHEMERAL_MODE='False'

to prevent auto-starting an ephemeral server; otherwise remove it for 2.x.