Just drawing your attention to a change we're currently working through on github. There are more details on my post on python-committers at https://mail.python.org/pipermail/python-committers/2018-May/005404.html but this is the short version.
Microsoft has donated a significant amount of macOS, Windows and Linux build time on Visual Studio Team Services for CPython that we can use for PR and commit builds on github. We've hooked these up already, so you will see new checks on github pull requests (e.g. https://github.com/python/cpython/pull/6937 ). These are currently not required, but apart from some asyncio tests they appear to be totally stable and considerably faster than our current ones.
There are a few limitations still, which I'll be working with the VSTS team to resolve. Feel free to email me with any questions or suggestions.
And for complete openness, Microsoft hopes that this will be good publicity for VSTS. If you have any examples of this working (e.g. you adopt it for other projects, start using it at work, etc.) then please pass those on to me as well. It will help convince then to keep giving us free resources :)