I have heard it was pretty rough. I extricated myself after the technical interview after reading up on process and conditions seemed like interesting work but not remotely altruistic in its goals. I hope you found something much better.

Is Palantir not considered to be private sector?

It is. I did not work for palantir though, I worked as an intelligence anaylst in public sector who used Palantir in my job. Palantir does not provide analysts, generally, they just sell the software. The forward deployed engineers help install and instruct, and sometimes they have people come on site to walk through analytical use cases, but generally they don't employ many, if any, actual full-time intelligence analysts, from what I saw.

Palantir is private sector, but they sell to governments.