How do you version and deprecate endpoints in a RESTful API that serves financial data?

Versioning a RESTful API that handles financial data is critical for maintaining data integrity, regulatory compliance, and backward compatibility. The most common strategy is URI versioning, e.g., /v1/accounts, which makes the version explicit and easy for clients to discover. Header-based versioning (Accept: application/vnd.company.v1+json) or query parameters (api_version=1) are alternatives when you want to keep the URI clean. When deprecating an endpoint, first announce the change in release notes and via API documentation. Provide a clear deprecation timeline (e.g., 6 months) and offer a migration guide. Keep the old endpoint alive but return a 410 Gone status and a message directing clients to the new version. Use feature flags or a gateway to route traffic to the new implementation while monitoring for errors. Finally, update your OpenAPI/Swagger spec to mark the old endpoint as deprecated and ensure automated tests cover both versions. This approach balances stability for existing clients with the flexibility to evolve the API.