Sunset Policies and Client Migration

A deprecated API feature can remain operational for years unless someone defines how support ends. A deadline alone is not enough: consumers need a usable replacement, a way to verify their changes, and clear behavior when the old interface stops serving requests.

A sunset policy defines the conditions and commitments for retiring a supported interface. Client migration is the work of moving integrations to the replacement without losing correctness or continuity.

This chapter connects those responsibilities through a fictional order API, from selecting a deadline to verifying that retirement is complete.