Per-model input/output price history (JSON or CSV via Accept header)

Returns one time series of input/output USD prices for any tracked model; every point is resolved with the same rule as price-at and carries its own source, so a single series mixes provenance. Instants where the confirmed revision in force attests the model are manifest-sourced (source=manifest, cross-linking revisionVersion, methodologyVersion and metadataHash); every other instant falls back to the live catalog's temporal history (source=catalog). Consecutive points repeating the same source and prices are collapsed; granularity defaults to per-revision, daily and weekly carry forward the last observed price, and catchup revisions whose manifest is unavailable are surfaced via unavailableRevisions. Models with neither an attested appearance nor a catalog price return 404. 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.