How does this website make money?

I was taking a course on Udemy, which was totally free and awesome when I realized that I had created a Codeacademy account a couple years ago. Then, I realized Udemy was totally free and hadn’t asked me for money once. Now, I’m looking over this website and it seems to be all free.

Is it really all free?


Codecademy courses are free,
Codecademy has extra content: projects & quizzes, support from advisors which is paid content.