The wire schemas load on the first message per protocol version and the
pydantic validators build on first use, which keeps imports fast but puts a
one-time bill on a process's first messages. A long-running host that
would rather pay that at startup than on its first request had only a DIY
recipe of model_rebuild() loops.
mcp_types.methods.warm(version=None, *, everything=False) is the supported
version: with no argument it builds the version-independent set (the
exported mcp_types models, the JSON-RPC envelopes and the routing union
adapters, ~50 ms); with a version it also imports that version's wire
package and builds the routing surface a connection at that version uses
(so its first messages then build nothing); everything=True covers every
known version. Model classes are always completed before the adapters
that reference them, so no schema is generated twice, and repeat calls
are no-ops. It returns a small WarmReport for logging and is re-exported
as mcp.warm. Nothing in the SDK calls it. The import-cost docs recipe now
uses it.
Max Isbey
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