Whew. A whole month after the first release and I've managed to solve this for my own situation. Just signed up to share in case anyone else happens to be in a similar situation, especially as the Xcode beta's download UI and error messages weren't very helpful for me. Situation: I've been using iPhone's Personal Hotspot as my primary internet connection for several weeks (recently moved to a new apartment and 400mbps+ download is more than enough for my needs.) Solution: Temporarily disable optimized battery charging on iPhone. Side note — if there are any Apple engineers on the relevant team reading, I'd consider this to be unexpected behavior. Xcode has had no problem downloading much larger files such as Simulator runtimes.