I have a few window frames that have a 1/2" to 3/4" gap that I need to fill. I can't replace the windows right now, so it needs to last a few years but still keep cool air in and busy street noise out.

I'm thinking clear silicone caulk, but the gaps are pretty large for caulk so I'm reaching out to see what the best option is. Thank you! Pictures with Jerry-rigged solutions below. I stuffed foam into the largest gap and covered it with packing tape. Just packing tape in the second pic.

Try some Window Glazing

Use backer rod in the gaps around the window and caulk over the backer rod. You could also spray foam it but I wouldn't unless you've done it before.

Minimal-expanding window spray foam. Follow directions (spray sparingly). Cut flush with straight razor. Cover with window trim.