What it is
The job it was built for, and the job it is not for.
GPT-5.6 Sol Pro is not a separate model, it is the same underlying GPT-5.6 Sol running with `reasoning.mode` set to `pro`. The job it is built for is the harder end of the work: multi-step problems where a first-pass answer tends to be wrong in ways that are expensive to catch. It is not the setting you want for routine classification, extraction or chat, where the standard Sol configuration does the same work for less.