Also had this issue. On one machine the 3.xx gb update started, took ages, then shortly before finishing restarted, and ended in a loop. On an other fresh Catalina machine, it‘s already taking 13h to download and still not finish. Estimating about 20h to download in total. No clue if this will even get installed in the end. I also get an error message if I try to install the CommandLineTools via Terminal (not able to find it this way). Hopefully this is getting resolved quickly. Cheers

Yep would also like to know instead of getting the error message that it is currently not available. Since I need them I now downloaded the Xcode 12.1GM CommandLineTools from the Developer Account Download Section. But would be nice if xcode-select --install would work...