Do I have to pay for Mac OS upgrade?

Yes, all updates of full Mac OS versions are free. Thus, if you are planning to update to the full version of OS Catalina in September, you can do it for free. The only thing you can pay, if you need this option, is the Developer Preview of Mac OS beta version.

Is Mac operating system free?

Apple has made its latest Mac operating system, OS X Mavericks, available to download for free from the Mac App Store. Apple has made its latest Mac operating system, OS X Mavericks, available to download free from the Mac App Store.