TW Model Price Index

Methodology

The index tracks the blended list price (3 parts input to 1 part output, per million tokens) of every model on our pricing page. Each week's movement is the geometric mean of price changes across models priced in both that week and the week before, chained onto the previous value and set to 100 in the first week with data. A newly listed model joins without moving the index; only price changes do. In its first months the index covers only a handful of models, so a single price change moves it much more than it would today. Prices come from LiteLLM's public model price list, sampled weekly before October 2026 and daily since.