API Version

Overview

API Version is an identifier for a defined release or compatibility boundary of an API’s contract and behavior. It is used to let providers evolve interfaces while clients select and support a known set of expectations. It differs from an application release number, which may change internally without changing the public API version.

A typical implementation works as follows: The provider exposes the version through a path, header, media type, hostname, or negotiated protocol and publishes its contract and support policy. Changes to API Version should be checked against older clients, stored payloads, enum growth, default behavior, and retry assumptions.

Common risks include unclear version selection and inconsistent endpoint versions. Important failure modes include unclear version selection, inconsistent endpoint versions, hidden behavioral changes, and indefinite support. These failures can create fragmentation and breakage.

Core controls require teams to use a documented strategy, maintain compatibility within stated boundaries, publish changes and dates, test supported versions, and measure usage. Testing API Version should cover malformed input, denied access, rate limits, timeouts, duplicates, asynchronous completion, and version changes.

Operational evidence should include API version, release date, contract revision, supported clients, deprecation status, environment, and traffic share. API Version should be documented alongside API Version Compatibility, API Lifecycle, and API Deprecation. For API Version, the application should preserve a correlation path from request construction through response, asynchronous completion, and final business state.

Data handled by API Version should use documented types, units, timestamp rules, nullable fields, and enum behavior to prevent silent interpretation errors.