Changelog

5.134.1

(fix): The OpenAPI error-responses setting now replaces a pre-existing components.schemas entry of the same name when nothing references it anymore once the 4xx/5xx responses have been rewritten (the common case: a legacy error body under apply-to: all), so specs that ship their own TwilioServiceErrorResponse-style schema no longer need a per-spec overlay to remove it first. If the legacy schema is still referenced (a 2xx body, another schema, apply-to: untyped), the error now lists the offending JSON Pointers.

5.134.0

(fix): Fix OpenAPI allOf required-ness when a branch lists a property in required that is defined only by another (parent) branch. The property is now required on the composed type, so a nullable: true property becomes required-nullable and round-trips null in generated SDKs. Multi-level allOf chains are handled; properties required in no branch stay optional.

(fix): When an OpenAPI allOf parent is inlined into a type or request body because of a property conflict, the inlined properties now keep their metadata (readOnly filtering on write request bodies, x-fern-property-name, x-fern-audiences, deprecated, access, and XML encoding) instead of being copied as bare type references.

(fix): Fix fern check reporting duplicate properties when an OpenAPI schema with a nullable: true allOf parent lists parent-defined properties in its own top-level required. The nullable parent is now inlined (instead of being kept in extends alongside the redeclared property).

(feat): The OpenAPI importer used for SDK generation now honors 4XX and 5XX wildcard error responses instead of silently dropping them. Wildcards are imported as ClientRequestError (covers 400-499) and ServerError (covers 500-599), and a concrete status code declared alongside a wildcard always takes precedence. Fern Definition errors now accept status-code: 4XX / status-code: 5XX as well.

5.133.0

(internal): The CLI now sends an X-Fern-Agent header on every FDR, Venus and Fiddle request (and tags its own telemetry events with agent) when run from a coding agent (Claude Code, Cursor, Codex, Devin, Gemini CLI), so agent-driven usage such as docs publishes can be measured separately from human usage.

(fix): fern init --docs now produces a project that builds with no further edits. When no API definition exists in the fern folder, it scaffolds pages/welcome.mdx and points the navigation at it instead of emitting an api: item with nothing to render. fern check also reports a new api-section-has-definition error when an api: navigation item does not resolve to any API definition, instead of passing and then failing at build time.

5.132.0

(feat): Add an error-responses OpenAPI setting that applies a single error body schema (e.g. RFC 9457 Problem Details) to the 4xx/5xx responses of every operation in a spec, so per-spec overlays are no longer needed to type error responses.

api:
  specs:
    - openapi: openapi.yml
      settings:
        error-responses:
          schema: errors/problem_details.yml   # file path or inline schema
          name: ProblemDetails                 # generated type name (defaults to the schema title)
          apply-to: all                        # `all` (default) or `untyped`
          ensure:
            - status-code: 422
              methods: [post, put, patch]

apply-to: all replaces the body of every error response; untyped only fills in responses that declare no body schema. ensure adds the listed status codes to operations that do not declare them.