I feel like there were 3 steps:

- 2008-2012 Python 3 becoming usable (byte formatting, six library)

- 2012-2016 Libraries (Django, etc) becoming compatible

- 2016-today Applications (Trac, Ansible, Chrome[1], etc) becoming compatible.

[1] https://bugs.chromium.org/p/chromium/issues/detail?id=942720