I still use Opus 4.6 and 4.8 regularly, as I often find Opus 5 too verbose (and Fable too expensive). You can add them back to the /model picker using the "modelPicker" array in settings.json
You can also simply type `/model claude-opus-4-8` and it'll work. The interactive picker is not the full set of models accessible through the /model command.
caveman mode?
Sensible mode
/i-have-adhd or /the-writing-whip are also pretty good as well with Opus 5!