Are MITx courses free?

Excuse me, I was wondering if you could clarify something for me. I've been hearing a lot about MITx courses and I'm considering enrolling in one, but I'm a bit unsure about the cost. So, my question is: are MITx courses free to take, or do I have to pay a fee to access them? I'd really appreciate it if you could provide me with some clarity on this matter. Thank you in advance for your help.