This is part of Medium’s updated Partner Program in which for those who are part of the program, they will be given the option of hiding their posts behind a paywall (see screenshot above) so that only those who are willing to pay will be able to read it. However according to Medium, those who don’t pay can still access your content via a metered system, meaning that they only get a few “free” articles per month, after which additional access will have to be paid for.
In terms of payment, Medium claims that this will depend on the number of “claps” you get. “For the creators in the program, each month you will be paid based on the level of engagement your stories get from Medium members. Essentially, we look at the engagement of each individual member (claps being the primary signal) and allocate their monthly subscription fee based on that engagement.”
This means that there is no set amount of money a creator can make as it will depend on the engagement level of the content, which we guess makes sense and is also pretty similar to how most ads on websites work. It is an interesting feature and also another way for creators to make money, apart from accepting donations via PayPal or getting subscribers on Patreon.