Finished the Palantir frontend SWE loop a few weeks ago for a role on one of their Foundry product teams. Sharing because I couldn't find anything specific to frontend when I was prepping.
Full disclosure: I did not get an offer. But the process was well-run and the feedback was actually useful, so I'm posting anyway.
The loop: recruiter screen, one Karat technical screen, then three onsite rounds (two technical, one behavioral/HM).
Technical round 1: pure coding. No frontend at all. Graphs, hash maps, standard algorithmic problems. Medium difficulty. I was honestly a bit caught off guard expecting React or DOM questions. They treat frontend SWE as SWE first. The interviewer said explicitly they don't differentiate frontend/backend in the core coding bar.
Technical round 2: more applied. This one did have frontend flavor. We worked through building a data grid component from scratch. No framework. Vanilla JS. They wanted to see how I structured state, how I thought about performance with large datasets (virtualization came up), and how I handled edge cases like empty states and loading. This was the more enjoyable round honestly.
What I got feedback on: My data structures in round 1 were fine but I didn't communicate tradeoffs proactively. When I chose an approach I explained what it did but not why I wasn't using an alternative. That's a pattern they care about apparently.
Behavioral round: Standard Palantir questions. Ambiguity, mission fit, working under pressure. The HM was sharp and the conversation felt real, not checklist-y.
Frontend stack at Palantir: From what I gathered, Foundry is TypeScript/React heavy. Blueprint.js is their internal component library and it's open source, so you can actually look at it beforehand which I recommend.
Total comp quoted for the role (senior SWE, NYC) was around 290-320k depending on refresh. I didn't make it to the offer stage so I can't confirm, but that's what the recruiter said during the pre-loop conversation.