Agave americana leaves have gone yellow

I am afraid your Agave is dead. I lost many of mine this past Winter.. Keep it for a while just in case it recovers.

Have you checked the soil for grubs?

Hi Gray, I have several of these that have been outside in the frost but they are bigger than yours. The outer leaves have gone yellow or brown but the inner ones are still green. You may find that the centre is still alive and will regrow. I think its just frost damage. The bigger they are , the better they survive. One I put under a tree is still OK.
Hope yours recovers!