It's supposed to be possible to switch to VS toolchains that are not yet the default by setting DEPOT_TOOLS_WIN_TOOLCHAIN_PRERELEASE=1 and running "gclient runhooks". However this doesn't work. The requested toolchain is noticed, but then ignored. It was necessary for me to set "force = True" in the Update function in build\vs_toolchain.py before "gclient runhooks" would have the desired effect.

I'm sure this used to work.