Claude versions? Maths notation?

(1) The model choice popup menu previously included Sonnet 3.7, although I couldn’t get it to work. Instead, v. 3.5 is not listed twice in the menu by mistake. (2) Is Sonnet 4 coming soon? (3) Sonnet 3.5 doesn’t seem to be able to write proper Maths notation. It really means that for Maths the only option at present is still GPT4.1. (Again GPT-5 mini doesn’t work at all for me.)