The AI Models Index keeps tabs on premium releases from 15 top labs since 2023,...

https://holdensimpressivethoughts.lumenforgex.com/posts/why-did-gpt-6.1-sol-improve-after-gpt-6-sol-regressed

The AI Models Index keeps tabs on premium releases from 15 top labs since 2023, with verified dates and blind-vote accuracy checks. Updated every two weeks, it shows a 56% improvement rate between GPT-5.1 and GPT-5