After sticking it into CharGPT I can tell you it's neither. The word upmost is coming from is a form of the compound verb ἐκπονέω.

* ἐκ- = “out,” “thoroughly,” “to the end”

* πονέω = “to labor,” “to toil,” “to work hard”

I can actually read Ancient Greek. LLMS are really bad at it.

> * ἐκ- = “out,” “thoroughly,” “to the end”

ἐκ is more motion away from something. It's often an intensifier in verb compounds but not really as a standalone preposition.

Ancient Greek is a very different language from English. I've found people who try to brute force it by looking up individual words without a knowledge of the grammar end up with a worse understanding of a text that someone who just reads in translation.

I trust a lifelong dedicated Ancient Greek Papyrologist to do a better job here than ChatGPT.