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Add a client-side response cache honoring SEP-2549 caching hints (#3023)

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Max 2026-06-30 11:31:06 +01:00 • committed by GitHub
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docs/migration.md
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@ -427,6 +427,10 @@ On `ClientSession`, `call_tool` / `get_prompt` / `read_resource` still return th
For protocol 2026-07-28 over Streamable HTTP, a tool's input-schema property may carry an `x-mcp-header` annotation. When a tool the client has listed is called, each annotated argument is mirrored into an `Mcp-Param-<name>` request header (string verbatim, integer as decimal, boolean as `true`/`false`, base64-sentinel-wrapped when not header-safe; `null`/absent arguments are omitted). The argument is also left in the request body. `list_tools` caches a tool's annotations, so list a tool before calling it to enable mirroring; a tool the client never listed emits no `Mcp-Param-*` headers. Other transports ignore the annotation.
### `Client` verbs may serve cached responses ([SEP-2549](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2549))
On protocol 2026-07-28, servers attach caching hints (`ttlMs`, `cacheScope`) to the cacheable results, and `Client` now honors them: `list_tools`, `list_prompts`, `list_resources`, `list_resource_templates`, and `read_resource` may serve a cached response instead of making a round trip, for as long as the server's `ttlMs` says the result is fresh. With the default configuration, servers that send no hints, including every pre-2026 server, see identical call-for-call behavior, because hint-less results are not cached (a `CacheConfig.default_ttl_ms` above zero caches them too). Pass `Client(..., cache=False)` to disable the cache and restore v1 behavior exactly; per-call control (`cache_mode`) and configuration (`CacheConfig`) are described in [Caching hints](advanced/caching.md).
### Server extensions API ([SEP-2133](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2133))
`MCPServer` now accepts opt-in extensions that bundle MCP behaviour behind a