https://api.kit.com/v5/.
What unstable means
- A V5 endpoint can change in a breaking way, or be removed, without a deprecation period.
- Every change to a documented V5 endpoint is in the changelog under the API V5 tag, so check it before you update a client. The changelog also has an RSS feed.
- When a V5 endpoint is ready for stable use, we’ll announce it in the changelog.
How V5 relates to V4
V5 only has endpoints that are new or that change how a V4 endpoint works. Everything else stays on V4, so an integration that uses V5 will usually call V4 too, and mixing the two versions is expected. A V5 endpoint doesn’t change its V4 counterpart: V4 keeps its existing behavior.What V5 shares with V4
- Authentication: the same API keys and OAuth access tokens work for both versions. There are no separate V5 credentials or OAuth flow.
- Rate limits: V4 and V5 requests count against the same rate limit for each access token or API key.
- Errors: errors use the same
errorsarray and the same status codes. - Pagination: list endpoints use the same cursor-based pagination.
Telling V5 responses apart
V5 responses carry anX-Kit-API-Stability: unstable header, including authentication, validation and rate-limit errors. A client or an AI agent that never reads these docs can still tell it’s talking to an unstable version. V4 responses don’t carry the header.