Is the word 'Hitherto' outdated? [closed]

Merriam-Webster Unabridged does not flag hitherto as "archaic."

Macmillan does mark hitherto as "very formal" but it's by no means outdated.

Whoever marked you down for using an "archaic" word is wrong (unless perhaps you were using hitherto in an informal context).

(Disclaimer: I read enough fantasy literature that hitherto seems rather ordinary to me.)

Anecdotally, yes, I would consider it archaic, and if I heard you use it I'd either think you were being pretentious, or that you were deliberately joking about speaking in a pretentious manner.

For reference, I'm a college educated American in my 40s.

As for replacements, I would just use "up to now" or "up till now". "yet" also works in some contexts.

Edit: To further emphasize, despite my education and reasonably broad reading habits, I'm not sure that I could have correctly defined "hitherto" until encountering this question, so this is about more than just trying to avoid seeming old-fashioned. I think using this term outside of certain technical contexts means you will not be widely understood by a general audience.