everyone It's been bothering me for a while - when someone asks 'what are you up to?' - i think it concerns the present continous tense or nearby future (plans) as in 'what are you up to today?'. I'm wondering if this kind of structure could be classified as any of the existing tenses. Thank you in advance and best regards :)
Grammatically speaking, "what are you up to?" is the present simple.
To be up to sth. - to be doing sth. (the Cambridge Dictionary): What are you up to? (=What are you doing?) - Nothing.
You are right saying that it's about the moment of speaking but this meaning is in the very phrase "to be up to something". By the way, we can't use it in the present continuous because the verb "to be" describes a state here.