He has both earned (as a software consultant) and been awarded fairly large sums of money in the past, and has purposefully lived inexpensively. Not sure if he presently has any income or not. As far as I know, neither the FSF nor MIT paid him since the early 1980's.

He has given paid talks for the last decade or two I believe.

Considering he was sleeping on a mattress in a MIT office, hopefully he saved a good portion of that in a bank account. He will also be eligible for social security and Medicare at his age, assuming he had enough working years in the social security system to qualify.

It's kind of sad given that probably all the FAANG companies wouldn't exist (yet) if it wasn't for his work.

You make it sound like only RMS' contributions were significant for our current state of software.

There are a lot of people with significant contributions without which the world wouldn't be in its current state.

Yes, but RMS seems to be at the root of it all.

For example, Linux depends on gcc and binutils and other GNU software, and many other software does.

He won that MacArthur award that came with money. He also owns a home in Cambridge that he rents out. Maybe social security as well.