Version Packages (beta)

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main is currently in pre mode so this branch has prereleases rather than normal releases. If you want to exit prereleases, run changeset pre exit on main.

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Releases

@modelcontextprotocol/server@2.0.0-beta.3

Minor Changes

• #2420 7635115 Thanks @felixweinberger! - Add runtime-neutral Bearer authentication to @modelcontextprotocol/server:
  requireBearerAuth gates web-standard fetch(request) hosts (Cloudflare
  Workers, Deno, Bun, Hono), built on the exported verifyBearerToken and
  bearerAuthChallengeResponse pieces, with OAuthTokenVerifier now defined
  here. The Express middleware adapts the same core and is unchanged in
  behavior, except that WWW-Authenticate challenge values are now RFC 7235
  quoted-string sanitized (quotes and backslashes escaped, control and
  non-ASCII characters replaced); @modelcontextprotocol/express re-exports
  OAuthTokenVerifier as before.

• #2422 61866d7 Thanks @felixweinberger! - Add runtime-neutral OAuth discovery serving to @modelcontextprotocol/server:
  oauthMetadataResponse serves the RFC 9728 Protected Resource Metadata and
  RFC 8414 Authorization Server metadata documents from web-standard
  fetch(request) hosts, built on the exported
  buildOAuthProtectedResourceMetadata, with
  getOAuthProtectedResourceMetadataUrl now defined here. The Express metadata
  router adapts the same core and is unchanged in behavior; the insecure-issuer
  escape hatch is an explicit dangerouslyAllowInsecureIssuerUrl option in the
  neutral core instead of a module-scope environment read. The web-standard
  matcher validates lazily so unmatched traffic always falls through, tolerates
  a trailing slash, supports HEAD, and marks reflected CORS preflights with
  Vary.

Patch Changes

• #2431 1b90c96 Thanks @morluto! - Fix the CommonJS validators/ajv subpath so reading the exported Ajv class no longer throws ReferenceError: import_ajv is not defined. The subpath now re-exports the bundled provider's concrete Ajv value in CJS output, matching the existing ESM behavior.

• #2441 561c6d8 Thanks @felixweinberger! - POSTs whose Content-Type media type is not application/json are now
  rejected with 415 Unsupported Media Type; the header is parsed instead of
  substring-matched. Previously any value merely containing the substring
  passed the check (for example text/plain; a=application/json), case
  variants were wrongly rejected, and the 2026-07-28 entry did not inspect
  Content-Type at all — requests with a missing or non-JSON header that used
  to be served on that path now also answer 415. Values with parameters
  (application/json; charset=utf-8, including malformed parameter sections
  like application/json;) continue to work. SDK clients always send the
  correct header and are unaffected.

  The new isJsonContentType(header) helper is exported for transport and
  framework-adapter authors — custom entries composing the exported building
  blocks (classifyInboundRequest, PerRequestHTTPServerTransport) must apply
  it themselves. The hono adapter's JSON body pre-parse and the client's
  response dispatch now use the same parsed-media-type comparison.

• #2384 ce2f65d Thanks @felixweinberger! - instanceof on the SDK error classes (ProtocolError and its typed subclasses, SdkError/SdkHttpError, OAuthError, and the client's SseError, UnauthorizedError, and OAuth-client-flow error family — OAuthClientFlowError and its subclasses) now works across separately bundled copies of the SDK. The classes match by a stable brand (via Symbol.hasInstance and a registry symbol) instead of prototype identity, so a process that uses both @modelcontextprotocol/client and @modelcontextprotocol/server - a gateway, host, or in-process test - can check errors constructed by either package against the class re-exported by the other. Ordinary prototype-based instanceof is preserved as a fallback; user-defined subclasses keep plain prototype semantics. Notes: cross-bundle matching requires both copies to be at or after this release; brands assert identity, not field shape, across versions - keep reading fields defensively. As a side effect, a foreign-bundle SdkError used as an abort reason is now rethrown as-is instead of being wrapped as a RequestTimeout. Branded hierarchies additionally expose an explicit static guard, X.isInstance(value), that reads the same brand and narrows in TypeScript — an alternative for codebases that prefer predicate-style checks over instanceof. Also: UnauthorizedError now sets error.name to 'UnauthorizedError' (previously 'Error'), and per-package conformance tests enforce that every exported error class participates in branding. Version-negotiation probing now recognizes UnauthorizedError (previously a dead name-string check) and propagates it unchanged, so connect() on an auth-gated server rejects with the original UnauthorizedError (previously wrapped as the cause of an SdkError(EraNegotiationFailed)) — run finishAuth() and reconnect, and the retry probes with the token.

• #2425 e8de519 Thanks @Sehlani042! - Stop advertising validator provider classes from the root client/server type declarations. The provider classes remain available from the explicit validator subpaths.

@modelcontextprotocol/client@2.0.0-beta.3

Patch Changes

• #2431 1b90c96 Thanks @morluto! - Fix the CommonJS validators/ajv subpath so reading the exported Ajv class no longer throws ReferenceError: import_ajv is not defined. The subpath now re-exports the bundled provider's concrete Ajv value in CJS output, matching the existing ESM behavior.

• #2441 561c6d8 Thanks @felixweinberger! - POSTs whose Content-Type media type is not application/json are now
  rejected with 415 Unsupported Media Type; the header is parsed instead of
  substring-matched. Previously any value merely containing the substring
  passed the check (for example text/plain; a=application/json), case
  variants were wrongly rejected, and the 2026-07-28 entry did not inspect
  Content-Type at all — requests with a missing or non-JSON header that used
  to be served on that path now also answer 415. Values with parameters
  (application/json; charset=utf-8, including malformed parameter sections
  like application/json;) continue to work. SDK clients always send the
  correct header and are unaffected.

  The new isJsonContentType(header) helper is exported for transport and
  framework-adapter authors — custom entries composing the exported building
  blocks (classifyInboundRequest, PerRequestHTTPServerTransport) must apply
  it themselves. The hono adapter's JSON body pre-parse and the client's
  response dispatch now use the same parsed-media-type comparison.

• #2384 ce2f65d Thanks @felixweinberger! - instanceof on the SDK error classes (ProtocolError and its typed subclasses, SdkError/SdkHttpError, OAuthError, and the client's SseError, UnauthorizedError, and OAuth-client-flow error family — OAuthClientFlowError and its subclasses) now works across separately bundled copies of the SDK. The classes match by a stable brand (via Symbol.hasInstance and a registry symbol) instead of prototype identity, so a process that uses both @modelcontextprotocol/client and @modelcontextprotocol/server - a gateway, host, or in-process test - can check errors constructed by either package against the class re-exported by the other. Ordinary prototype-based instanceof is preserved as a fallback; user-defined subclasses keep plain prototype semantics. Notes: cross-bundle matching requires both copies to be at or after this release; brands assert identity, not field shape, across versions - keep reading fields defensively. As a side effect, a foreign-bundle SdkError used as an abort reason is now rethrown as-is instead of being wrapped as a RequestTimeout. Branded hierarchies additionally expose an explicit static guard, X.isInstance(value), that reads the same brand and narrows in TypeScript — an alternative for codebases that prefer predicate-style checks over instanceof. Also: UnauthorizedError now sets error.name to 'UnauthorizedError' (previously 'Error'), and per-package conformance tests enforce that every exported error class participates in branding. Version-negotiation probing now recognizes UnauthorizedError (previously a dead name-string check) and propagates it unchanged, so connect() on an auth-gated server rejects with the original UnauthorizedError (previously wrapped as the cause of an SdkError(EraNegotiationFailed)) — run finishAuth() and reconnect, and the retry probes with the token.

• #2425 e8de519 Thanks @Sehlani042! - Stop advertising validator provider classes from the root client/server type declarations. The provider classes remain available from the explicit validator subpaths.

@modelcontextprotocol/codemod@2.0.0-beta.3

Patch Changes

• #2419 79dc162 Thanks @felixweinberger! - Read the v2 package versions the codemod writes into migrated package.json files directly from the workspace manifests at build time, replacing the committed generated versions.ts (which went stale after every release and made source builds write outdated versions).

• #2420 7635115 Thanks @felixweinberger! - Add runtime-neutral Bearer authentication to @modelcontextprotocol/server:
  requireBearerAuth gates web-standard fetch(request) hosts (Cloudflare
  Workers, Deno, Bun, Hono), built on the exported verifyBearerToken and
  bearerAuthChallengeResponse pieces, with OAuthTokenVerifier now defined
  here. The Express middleware adapts the same core and is unchanged in
  behavior, except that WWW-Authenticate challenge values are now RFC 7235
  quoted-string sanitized (quotes and backslashes escaped, control and
  non-ASCII characters replaced); @modelcontextprotocol/express re-exports
  OAuthTokenVerifier as before.

@modelcontextprotocol/express@2.0.0-beta.3

Patch Changes

• #2420 7635115 Thanks @felixweinberger! - Add runtime-neutral Bearer authentication to @modelcontextprotocol/server:
  requireBearerAuth gates web-standard fetch(request) hosts (Cloudflare
  Workers, Deno, Bun, Hono), built on the exported verifyBearerToken and
  bearerAuthChallengeResponse pieces, with OAuthTokenVerifier now defined
  here. The Express middleware adapts the same core and is unchanged in
  behavior, except that WWW-Authenticate challenge values are now RFC 7235
  quoted-string sanitized (quotes and backslashes escaped, control and
  non-ASCII characters replaced); @modelcontextprotocol/express re-exports
  OAuthTokenVerifier as before.

• #2422 61866d7 Thanks @felixweinberger! - Add runtime-neutral OAuth discovery serving to @modelcontextprotocol/server:
  oauthMetadataResponse serves the RFC 9728 Protected Resource Metadata and
  RFC 8414 Authorization Server metadata documents from web-standard
  fetch(request) hosts, built on the exported
  buildOAuthProtectedResourceMetadata, with
  getOAuthProtectedResourceMetadataUrl now defined here. The Express metadata
  router adapts the same core and is unchanged in behavior; the insecure-issuer
  escape hatch is an explicit dangerouslyAllowInsecureIssuerUrl option in the
  neutral core instead of a module-scope environment read. The web-standard
  matcher validates lazily so unmatched traffic always falls through, tolerates
  a trailing slash, supports HEAD, and marks reflected CORS preflights with
  Vary.

• Updated dependencies [1b90c96, 561c6d8, ce2f65d, e8de519, 7635115, 61866d7]:

  • @modelcontextprotocol/server@2.0.0-beta.3

@modelcontextprotocol/fastify@2.0.0-beta.3

Patch Changes

• Updated dependencies [1b90c96, 561c6d8, ce2f65d, e8de519, 7635115, 61866d7]:
  • @modelcontextprotocol/server@2.0.0-beta.3

@modelcontextprotocol/hono@2.0.0-beta.3

Patch Changes

• #2441 561c6d8 Thanks @felixweinberger! - POSTs whose Content-Type media type is not application/json are now
  rejected with 415 Unsupported Media Type; the header is parsed instead of
  substring-matched. Previously any value merely containing the substring
  passed the check (for example text/plain; a=application/json), case
  variants were wrongly rejected, and the 2026-07-28 entry did not inspect
  Content-Type at all — requests with a missing or non-JSON header that used
  to be served on that path now also answer 415. Values with parameters
  (application/json; charset=utf-8, including malformed parameter sections
  like application/json;) continue to work. SDK clients always send the
  correct header and are unaffected.

  The new isJsonContentType(header) helper is exported for transport and
  framework-adapter authors — custom entries composing the exported building
  blocks (classifyInboundRequest, PerRequestHTTPServerTransport) must apply
  it themselves. The hono adapter's JSON body pre-parse and the client's
  response dispatch now use the same parsed-media-type comparison.

• Updated dependencies [1b90c96, 561c6d8, ce2f65d, e8de519, 7635115, 61866d7]:

  • @modelcontextprotocol/server@2.0.0-beta.3

@modelcontextprotocol/node@2.0.0-beta.3

Patch Changes

• #2441 561c6d8 Thanks @felixweinberger! - POSTs whose Content-Type media type is not application/json are now
  rejected with 415 Unsupported Media Type; the header is parsed instead of
  substring-matched. Previously any value merely containing the substring
  passed the check (for example text/plain; a=application/json), case
  variants were wrongly rejected, and the 2026-07-28 entry did not inspect
  Content-Type at all — requests with a missing or non-JSON header that used
  to be served on that path now also answer 415. Values with parameters
  (application/json; charset=utf-8, including malformed parameter sections
  like application/json;) continue to work. SDK clients always send the
  correct header and are unaffected.

  The new isJsonContentType(header) helper is exported for transport and
  framework-adapter authors — custom entries composing the exported building
  blocks (classifyInboundRequest, PerRequestHTTPServerTransport) must apply
  it themselves. The hono adapter's JSON body pre-parse and the client's
  response dispatch now use the same parsed-media-type comparison.

• #2445 78fabea Thanks @felixweinberger! - Document composing the host and origin validation guards in front of toNodeHandler for hand-wired node:http servers, matching the protected wiring the examples and serving guide now demonstrate.

• Updated dependencies [1b90c96, 561c6d8, ce2f65d, e8de519, 7635115, 61866d7]:

  • @modelcontextprotocol/server@2.0.0-beta.3