MCP TypeScript SDK 2.2.0 makes machine-to-machine OAuth providers declare an issuer and rejects authorization-server mismatches before sending a token request. List calls such as `listTools()` and `listResources()` now follow pagination automatically when callers omit a cursor. The security check closes an identity ambiguity, while auto-pagination can change latency, request volume, memory use and returned result size in existing clients.
MCP SDKs 2.3 tighten transport and OAuth boundaries
2026-09-29Verified announcementTRIAL
MCP TypeScript and Python SDK 2.3 releases tighten connection, OAuth and payload boundaries. TypeScript redirects stay same-origin by default, can validate token audiences and enforce tool-input element limits; server and transport objects now have a one-request lifecycle. Python rejects invalid MCP headers during registration and caps SSE events at 1 MiB by default.
What this means for you
For MCP client and gateway teams, the security defaults are useful but the transport lifecycle can break shared server instances. Test redirects, audiences, oversized payloads and reconnection before rollout.
Evidence & related material
MCP TypeScript and Python SDK 2.3 tighten redirect, audience, connection-lifecycle and SSE payload boundaries.
MCP TypeScript SDK 2.4 adds experimental Skills and tighter protocol validation
Subsequent changes
TypeScript and Python SDK 2.3 tighten transport, OAuth and payload boundaries.
MCP TypeScript SDK 2.4 adds experimental Skills and tighter protocol validation
Technical details & scores
| Versions | TypeScript 2.3.0 / package line 1.32.0; Python 2.3.0 |
|---|---|
| Typescript Security | same-origin redirects by default; expectedResource audience validation; maxToolInputElements |
| Typescript Lifecycle | server and transport are single-connection/single-request objects |
| Python Security | invalid x-mcp-header rejected during registration |
| Python Limits | SSE event default maximum 1 MiB, configurable |
| Compatibility Risk | shared server/transport reuse and oversized SSE payloads can break |
| Latest Version | 2.4.0 |
| Skills Extension | Servers can publish skill folders and clients can list, read and verify them; attach wiring remains experimental. |
| Upgrade Boundary | Invalid x-mcp-header numeric parameters and URI schemes are rejected; older structuredContent wrappers change. |
| Time Basis | GitHub release published 2026-10-23T18:32:25Z. |
Technical impact 3
Engineering value 4
Adoption signal 3
Maturity 4
Verification cost 2
Risk 2