MCP 2026-07-28 规范发布：协议转向无状态架构

模型上下文协议（MCP）发布了2026-07-28版本规范，实现了协议设计的根本性转变。1新版本将MCP从有状态的双向协议改造为无状态的请求/响应模式，使得每个请求都可以路由到不同的服务器实例上，从而支持轮询负载均衡。1此次更新涉及TypeScript、Python、Go、C#等Tier 1 SDK，这些SDK的月下载量接近5亿次，其中TypeScript和Python SDK的总下载量均已超过10亿次。1

核心架构调整包括删除initialize/initialized交换和Mcp-Session-Id header，1转而引入server/discover RPC使客户端能够发现服务器能力。1方法和工具名称现在通过Mcp-Method和Mcp-Name HTTP头传输，1多轮请求（MRTR）机制取代了之前需要保持开放流的服务器初始化请求。1列表响应增加了ttlMs和cacheScope字段以支持客户端缓存策略，1授权服务器须按RFC 9207返回iss参数，客户端在兑换代码前必须完成验证。1

此外，Dynamic Client Registration（DCR）正式弃用，改为Client ID Metadata Documents（CIMD）方案。1Roots、Sampling和Logging等功能至少保留12个月兼容期后将移除，1HTTP+SSE传输模式也已正式弃用。1

The Model Context Protocol (MCP) has released its 2026-07-28 specification, introducing a fundamental architectural shift from a stateful bidirectional protocol to a stateless request-response model 1. This transformation enables each request to be routed to different server instances, supporting round-robin load balancing while maintaining protocol consistency 1.

The update eliminates the initialize/initialized exchange and removes the Mcp-Session-Id header, streamlining the connection handshake 1. In their place, the specification introduces a new server/discover RPC endpoint that allows clients to dynamically discover server capabilities 1. Method and tool names are now transmitted via HTTP headers—Mcp-Method and Mcp-Name—rather than embedded in request payloads 1. Multi-Round-Trip Requests (MRTR) replace the previous server initialization pattern that required maintaining open streams 1.

Several features enhance caching and security in the new architecture. List responses now include ttlMs and cacheScope parameters to support client-side caching strategies 1. Authorization servers must return the iss parameter in compliance with RFC 9207, and clients are required to validate this parameter before exchanging authorization codes 1. The specification formally deprecates Dynamic Client Registration (DCR) in favor of Client ID Metadata Documents (CIMD) 1.

MCP Tier 1 SDKs—covering TypeScript, Python, Go, and C#—have been updated to implement the new specification 1. The Tier 1 SDKs collectively generate nearly 500 million monthly downloads, with TypeScript and Python SDKs each exceeding 1 billion total downloads 1. Deprecated features including Roots, Sampling, Logging, and HTTP+SSE transport will maintain backward compatibility for a minimum of 12 months 1.