API Versioning

API versioning is the practice of managing changes to a public API so that existing clients keep working when you evolve it. Because other people's apps, mobile clients, and integrations depend on your response shapes, you can't just rename a field or drop an endpoint — that breaks them silently. Versioning gives you a way to ship breaking changes under a new version (v1, v2) while the old one keeps serving. Common strategies are URL-based (/v1/orders), header-based (Accept: application/vnd.api+json;version=2), or query parameters. The broader discipline is distinguishing breaking changes (removing a field, changing a type) from backward-compatible ones (adding an optional field), and only bumping the version for the former. For AI/SaaS builders shipping a public or partner API, versioning plus a clear deprecation policy is what lets you move fast internally without breaking every customer. Practical note: version from day one even if you only have v1, and communicate deprecation timelines long before you remove anything.