A couple of buddies are planning a trip this Spring on a guided hunt. One of the options is a Yak, I’ve heard it’s great meat, is a 280 a good caliber to hunt with? Would I need a larger caliber? Tried searching online but didn’t find any info.

You're .280 will be fine. I'd suggest a good bullet. Perhaps a 160 gr accubond or the like. They are a good sized animal but I don't think they are excessively tough. Bullet placement is more important than a larger caliber. Good luck.
Bruce

Yak is my favorite meat. Having shot a few and guided hunters to many I am confident your 280 rifle is more than adequate. The 160 Accubond mentioned above is a good choice as is a 160 Partition and 150 Scirroco. There are lots of good bullets and as long as they are "controlled expansion" or some rendition of that they will be just fine. Talk to your guide extensively about shot placement. Best of luck!

I actually shot mine with a bow at 60#