I would struggle to ascertain the day-to-day difference between GPT-5.4 and GPT-5.5 tbh. Also, imho, Fable is highly hyped, I don't think it is dramatically better than Opus 4.8. Maybe my tasks and interaction with AI is relatively simple (i.e., lots of Rust programming, Linux system engineering stuff).

I haven't had enough time with fable, but I had to look back on how i worked with claude just 6 month ago to remind myself that it got a lot better.

Like i still used plan mode 6 month ago now I don't.

I would argue that with every model release we have a new learning phase.