Where the numbers come from

Methodology

Prices here are an append-only history, not a number that gets overwritten. When a provider cuts a price, the old figure doesn't disappear — a new dated price point is appended next to it, and every point records the source it was read from. That source string is stored on the row itself and shown on each model's snapshot table.

Anthropic figures I curate by hand and will stand behind. Other providers are best-effort: read from their public pricing pages, cross-checked by a daily OpenRouter sync, and occasionally lagging. When something's wrong it gets fixed and noted, not silently overwritten.

Historical points get a second pass. Each one is checked against Wayback Machine captures of the provider's pricing page from around its effective date — so the price recorded for March 2024 is the price an archived copy of the page actually showed in March 2024, not a number remembered later. Points that can only be dated approximately say so in their notes rather than pretending to precision.

That pass turns up real corrections — cached-input rates and output prices seeded a notch off, and price cuts that had gone unrecorded — each now fixed against the archived page that showed it. It also leaves a few honest judgement calls, flagged in a point's note rather than hidden: a price whose value is confirmed but whose exact change date falls in a gap between captures is recorded as a bracketed range; a value corroborated only by secondary trackers — because the provider's own page archived as an empty, JavaScript-rendered shell — says so; and a small number of very recent or open-weight rates that no archived first-party page could confirm are kept but marked unverified, not dressed up as certain.

Acknowledgements

This record stands on work other people do, and they should be credited for it:

• The providers' own pricing pages — the first-party source for nearly every figure on this site. Each one is linked above, and on every price point it backs.
• The Internet Archive's Wayback Machine — historical prices are verified against its captures of provider pricing pages. Without the Archive there would be no checkable record of what these pages said in 2023.
• OpenRouter — a daily sync against its catalogue keeps current prices fresh across the long tail of models, and flags moves worth verifying first-party.
• The LiteLLM community pricing dataset — its version history is a map of when prices changed, used to discover historical changes worth backfilling. Discovery only: every change it surfaces is verified against an archived first-party page before it's recorded here.

If a price looks stale or wrong, the source is right there on the price point — check it, and tell me.