What is an API Deprecation?

A well-run deprecation follows a lifecycle: an announcement with a sunset date, a deprecation header or warning in responses so integrators notice programmatically (not just by reading a changelog), a migration guide to the replacement, and finally the hard cutoff where the old endpoint returns errors or is removed entirely. Skipping any of these steps — especially the advance warning — breaks integrations without recourse. Deprecation is unavoidable because APIs evolve: a data model changes shape, a security flaw requires a breaking fix, or a whole approach is superseded by something better. The discipline isn't in avoiding deprecation, it's in doing it predictably enough that consumers can plan around it instead of getting blindsided by a 404 in production. For any system that depends on third-party APIs, tracking deprecation notices is a real operational responsibility — a provider's sunset date for an old endpoint is effectively a deadline on your own integration code, and missing it means a silent outage the day the old version finally goes dark.