What is the REST API deprecation lifecycle management?

A structured deprecation lifecycle prevents breaking clients while allowing APIs to evolve. The process: 1. Mark deprecated: add the Deprecation: true header and Sunset: {date} header to responses, and document with a deprecation notice in the OpenAPI spec (the deprecated: true field on operation or parameter). 2. Communicate: notify API consumers via email, developer portal announcements, and changelog. Provide migration documentation with the new endpoint or field. 3. Monitor usage: use API gateway analytics to track deprecated endpoint/field usage by client. Do not remove until usage drops to zero. 4. Set sunset date: give clients a reasonable migration window — minimum 6-12 months for major API changes, longer for large enterprise clients. 5. Enforce sunset: on the sunset date, return 410 Gone instead of processing the request. The Link header can point to the replacement: Link: <https://api.example.com/v2/users>; rel="successor-version". Automated tooling should alert clients whose usage drops to zero of an upcoming sunset to validate the migration is complete.