Adapters

Every adapter does the same job: open an exchange for the request, apply what it says, report back. The core owns everything else — change registry, pipeline compilation, version resolution, sunsets, telemetry — which is why each adapter is a couple hundred lines of framework-specific glue.

The shared contract

Per request, in order:

1. Resolve — the adapter hands core the method, path, matched route (when the framework exposes one), and a header getter; core resolves the effective version and compiles (or cache-hits) the transform pipeline.
2. Gate — sunset headers go on the response; a version past its cutoff is answered 410 Gone right here, and a rewrite target re-dispatches.
3. up(body) — the request body is converted to the current shape before validation and the handler.
4. Handler — your code runs against the current shape only.
5. down(body) — the response is converted back to the pinned client's shape (downError for status ≥ 400).
6. finish() — exactly one telemetry event is emitted, off the request path.

Shared behavior across all HTTP adapters:

• JSON only, ≤ 1MB. Only application/json bodies under 1MB are transformed; multipart, binary, form-data, streams, and stream: "passthrough" routes pass through untouched.
• Identity is free. When no changes touch the route, or the client is at current, the pipeline is empty and all body work is skipped.
• Sunsets are automatic. Scheduled versions get Deprecation + Sunset headers on every response; past the cutoff the adapter answers 410 Gone itself. See Rewrites & sunsets.
• Invalid pins fail fast. A malformed version string returns 400 { "error": "invalid_api_version" } before any handler runs.
• Telemetry is opt-in. One event per request when a sink is attached; without an apiKey or a manually attached sink, versionless makes zero network calls. A sink error can never fail a request.

Pick your framework

Route matching

Adapters pass the framework's own matched route pattern when they can (Elysia ctx.route, Hono matchedRoutes, the route option of the Next.js and TanStack Start wrappers), so core's matcher never runs. Express middleware can't see the matched route, so core falls back to matching the raw path against the (small) set of routes that actually have changes. tRPC and oRPC skip paths entirely — changes are keyed by procedure (trpc:demo.userList).

Serverless

On Vercel (process.env.VERCEL), the batched telemetry sink runs in immediate mode and every adapter calls exchange.flush() after the response, so events survive the function freezing.