This was a real bug on our side: truss pulled in uvloop, which does not support Windows, so every Windows install failed. We fixed it and shipped the fix in 0.9.7, so run pip install truss==0.9.7 or newer and it should install cleanly. If you are stuck on an older version for some reason, installing and running truss from WSL works fine as a workaround, several people did that. Source: https://github.com/basetenlabs/truss/issues/856