2026-07-28 model input: direct integration or stateless MRTR
architecture decision
New server: call a model provider directly. Compatibility need: carry deprecated Sampling through MRTR.
client and host model
every POST includes _meta
protocolVersion: 2026-07-28
clientCapabilities: sampling
fulfill inputRequests
apply approval and budgets
validate model output
retry original method
fresh JSON-RPC id
inputResponses for this round
exact requestState echo
No initialize
No protocol session
No reverse request channel
stateless MCP server
discover + cached tools/list
version -32022 | capability -32021
round 1: pick files
resultType: input_required
sampling/createMessage embedded
round 2: summarize
validate first response
return next input_required
round 3: complete
resultType: complete
requestState
HMAC binds principal, args,
phase, and short expiry
1. tools/call, id 1
2. input_required + signed state
3. tools/call retry, id 2
4. next input_required or complete
Any server instance can process a retry because the request and integrity-protected state are self-contained.