$600/hr is the equivalent of about $1.2M/year salary. That's exceptionally rare. Unless you're being cheeky with "should be", I think you have beliefs that are misaligned with reality.

Hourly billing rate has to cover all the hours you can't bill for, PTO, health care, everything..

Most contractors I know don’t work 40hrs day, every week. Also if you look around at advice you’ll find that you shouldn’t quote an hourly rate, you should quote “for the job”. If you’re good and the work you’re doing is even mildly specialized you can get a job done quickly enough that the effective hourly rate is pretty absurd.

What counts as "independent expert in specialized field"? Because as an independent backend contractor (java/spring/scala/akka) that straddles the line between architectural consulting and staff augmentation (usually long-term contracts), I see real resistance to going above $200/hr since even in the bay area you can hire full teams from vendors at around that price point for man hours.

8*600 is $4800 per day. What kind of expert in what specialized field do you have to be to make that much? Can you give a specific example?

Seems below average for law firm partners [1], and there's a lot of them out there, so it doesn't surprise me at all that technical consultants with genuinely rare skills could command hourly rates like that.

[1] https://www.mlaglobal.com/en/knowledge-library/research/2018...

Has anybody ever seen such a thing in reality? I have seen quite a few consultants and nobody ever got even close.