GPT-5.6 Sol - not a new brain, but a new build
Sol is not a new base model trained from scratch. This has already been confirmed in the release discussion.
Base training is the stage where a model forms its foundation: language, knowledge, logic, world understanding, and the ability to solve tasks.
So GPT-5.6 is not a new foundation, but an improvement of the existing line: additional training, reasoning, tools, and operating modes.
The real revolution will start with a new base model.
Most likely, that will be GPT-6.