No you don’t. You can write and apply to the partner program without paying.
But it does make it easier as you can interact more with other writers.
For free you can write as much as you like.
But you can only read 5 articles behind the paywall.
I am paying the 5$ a month subscription as I also enjoy reading on Medium.
Cool :)
Can you share your Medium profile? I am curious to learn about your sucess. :)