In our district all kids are given the CogApt test in 3rd grade, free of charge. One of mine scored high enough for GATE program and one didn’t.
But if a standard IQ test shows a high IQ, you really have to take another test that focuses on higher IQ to say that you have an IQ of 160 or 170.
For example, my GATE kid didn’t miss any questions on the spatial or quantitative sections. So that test wasn’t hard enough to narrow down where she is, other than to place her in the “gifted” category. Which I had known she would be in from the time she was a toddler, so no surprises there for me.
I could pay for more testing, but didn’t see the point. I suspect most gifted people don’t go through that sort of testing either due to expense, access or lack of interest.