I play oboe in concert band and for marching band I play flute. Next year we will have 16 flutes and only 2 alto saxes. My band director has asked me to consider learning alto. If I do, I will still be playing oboe in concert band and I don't want learning a new instrument to hinder me from excelling at oboe. Will learning how to play alto sax screw up my oboe playing or not? Especially since it is in a different key.

Provided you are able to spend time practising both instruments there should be no problem. It might take a bit of time initially to get used to the change from one to another with the change of fingering, embouchure, breath requirements & pitch.

Good luck

Thank you for your advice.

Considering ive played Alto for two years and counting, i believe you would love it. It shouldnt affect your oboe playing as long as you practice both. The alto will introduce you to jazz which cannot be played on flute nor oboe. Have fun!