Per-model input/output USD price effective at a given ISO-8601 date

Resolves from the confirmed revision in force at the requested date when that revision attests the model (source=manifest, cross-linking revisionVersion, methodologyVersion, metadataHash and family; observedAt is that revision's publishedAt). Otherwise the live catalog's temporal history answers (source=catalog, observedAt is the price row's own observedAt, family may be null). Returns 404 only when the model is untracked, or when neither the attested manifest nor the catalog holds a price at that date. Models are identified by the canonical vendor-prefixed id (openai/gpt-5.5). The key segment also accepts the bare model name; both name the same model, and the prefixed form needs the separator percent-encoded (openai%2Fgpt-5.5). An unknown vendor is a 422.