Why did pip upgrade from version 10 to version 18?

while running a pip install script I get the following warning:

 You are using pip version 10.0.1, however version 18.0 is available

This is very strange. Did the pip project just upgrade from version 10 to version 18? Why?


First point in the release notes:

  • Switch to a Calendar based versioning scheme.

https://pip.pypa.io/en/stable/news/

More about calendar versioning: https://calver.org/