This is an announcement from January 29th.
It says that only 0.1% of daily users use GPT-4.1, and the rest use 5.1 or 5.2.
It seems like GPT-4.1 was just announced not too long ago, and it's already ending.
Because new AI models come out every day, the transition to using new models is incredibly fast.
▶ Original source: https://openai.com/index/retiring-gpt-4o-and-older-models/
