Model and API contract

Claude Messages without a server prompt: preserves the native Anthropic Messages structures listed in these docs — thinking signatures, tool blocks, documents/citations, server-tool results, and usage.
server prompt: preserves the requested public model and provides the endpoint-aware compatibility described in the matrix; an unavailable capability returns an explicit error.
Fable 5 and 5.1: separate public models in Messages, Chat Completions, Responses and count_tokens without an actually applied server prompt. If a suitable prompt would apply, the request is rejected before billing; the existing Fable 5 ID does not switch to 5.1.
Service errors: temporary unavailability is returned as a neutral 503/504; retry with exponential backoff and respect Retry-After when present.

bash

curl -s https://api.guardrelay.ai/v1/messages \
  -H "x-api-key: $GUARD_API_KEY" \
  -H "anthropic-version: 2023-06-01" \
  -H "content-type: application/json" \
  -d '{"model":"claude-opus-5","max_tokens":16,"messages":[{"role":"user","content":"ping"}]}'

For every family, the requested public model ID determines the model name in the reply and its base tariff. An unknown ID returns 404; use an exact catalog ID.

Kimi. Four exact ids, no free spellings. If a different model answered upstream, the request is not delivered, the reserve is returned in full and you pay nothing: you get 502 kimi_model_mismatch.
Composer and Grok. Ten exact ids. Effort level and Fast mode are part of the id, so picking a model picks the level and the tariff at once; there are no fields for them.
Client tools do work for them on all three surfaces: see Client tools.
Unsupported for Composer/Grok: MCP, documents, native citations, structured outputs and count_tokens. Sampling and block-level cache_control are accepted without effect; they do not control generation or caching.

You can check it yourself: the model field in the response repeats the id you sent.

bash

curl -s -X POST https://api.guardrelay.ai/v1/chat/completions \
  -H "Authorization: Bearer $GUARD_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"model":"k3","max_tokens":16,"messages":[{"role":"user","content":"ping"}]}'

Model. The public id you send is the one that comes back and the one billing uses. Guard never lets a substitution through.
A different model. If another model answered upstream the request ends as 502 kimi_model_mismatch, the reserve is returned in full and no usage row is written. You pay nothing for that request.
Streaming. The model name is checked on the very first frame, before the answer reaches you.
Rate. Billing uses the published rate of the model you asked for. Confirmed current PRIVATE membership gives 25% off after cache pricing.
Surfaces. Kimi is served on all three: plain POST /v1/chat/completions, the Anthropic Messages protocol and the Responses protocol. The model guarantee is the same on each of them.

bash

curl -s -X POST https://api.guardrelay.ai/v1/chat/completions \
  -H "Authorization: Bearer $GUARD_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"model":"cursor-grok-4.6-medium","max_tokens":16,"messages":[{"role":"user","content":"ping"}]}'

bash

curl -s -X POST https://api.guardrelay.ai/v1/chat/completions \
  -H "Authorization: Bearer $GUARD_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"model":"composer-2.5","max_tokens":16,"messages":[{"role":"user","content":"ping"}]}'

Model and API contract

Public guarantees

Kimi, Composer and Grok

What Guard guarantees for Kimi

Documentation sections

On this page