OpenAI is removing text chat limits for all ChatGPT users, with Free and Go users getting GPT-5.6 Luna as the default model and a new Think button, while Plus and Pro users get an upgraded GPT-5.6 Sol model and a thinking slider.
From the source
The new GPT-5.6 Luna model will power this experience and will be the default model for Free and Go users, replacing GPT-5.5.
techcrunch.com