[Request] Historical data API

Hi,

The recent price changes for OpenAI models have shown that a single date entrypoint (latest) for pricing doesn't enough information for past data. Ideally, model costs should keep track of the timestamp of the change, so that tools that rely on this data and past agent sessions can match and determine the correct cost.

For example, PI agent linked to GitHub Copilot subscription isn't yet using the updated prices (even if Copilot does) when logging usage, leading to sessions that report much higher cost than actually billed.

Once the models.dev PR is merged to address costs changes, I'd like to still have access to the old pricing information as reference for my reporting tool, so that it can show older sessions with older price and newer ones with latest.

Is this something that could be built into models.dev?

Start by examining the pricing data and API entry points in models.dev to understand how the current latest-only model costs are represented and served. Define how timestamped price changes would be exposed and verify that historical sessions can retrieve the price applicable at their date while current sessions receive the latest price.