"However, by posting or transferring content to Medium, you give us permission to use your content solely to do the things we need to do to provide Medium Services, including, without limitation, storing, displaying, reproducing, and distributing your content. This may include promoting your content with partner companies or services for broader broadcast, distribution, or publication."

(They do say they won't sell your content to third parties without your consent, which is good.)

And you don't control if and when the terms of service change.