KIP-1265 — Mechanism for automatic detection of internal API usage

Accepted Kafka 4.4 Admin

Introduces a @PublicApi annotation and build-time enforcement mechanism that explicitly marks classes as public API and triggers compile or test failures when internal classes are inadvertently imported by or exposed through public APIs. Kafka's current convention (Javadoc presence = public) is implicit and unenforced, frequently resulting in internal classes leaking into public interfaces and being adopted by plugin developers without stability guarantees.

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