Whoop Senior iOS Engineer Interview Experience — Four Onsite Rounds, Rejected on System Design

I recently interviewed for a Senior iOS position at WHOOP (had a referral). Got rejected on the last round of the onsite, System Design. Didn't make it.

My overall impression of this company's interview process was really, really good. The company also supports H1B and green card, so I hope anyone who needs that applies quickly.

First, my impressions of WHOOP:

1. Very efficient — from the initial communication with the recruiter all the way through the middle rounds of interviews, everything went very smoothly.
2. I interviewed for an iOS role, and they don't test LeetCode at all — not even a little. All the technical rounds were about things related to actual work, which was very friendly for someone like me who's allergic to LeetCode.
3. In every interview except one, the engineers were very friendly and interactive.
4. When explaining code, it didn't need to actually run.
5. The recruiter explicitly said they support H1B (and premium processing), and would consider green card sponsorship after the first year's review.

Interview process:

Interview 1, Recruiter screening — a simple self-introduction, status/visa, relocation, that kind of thing.

Interview 2, Tech screening, with a mid-level engineer and a senior-level engineer — asked a lot about Swift Concurrency, very specific and interactive; if you'd actually done this kind of work and prepared well, you could answer it.

Interview 3, Onsite:

Round 1. Coding — a very simple MVVM task, implementing the rendering of a small screen.

Round 2. System Design — design a BLE command handler used in the app, where commands have to be sent one at a time: before the previous command's response comes back, or before it times out, the next command just has to keep waiting. Not an easy problem, but I had an approach, and eventually stumbled my way to something that worked — though clearly not sharp enough.

Summary: the diagram they gave for the problem was kind of odd (the terminology wasn't mobile-side terminology, it was firmware-side terminology), and both interviewers were stone-faced. I asked quite a few clarifying questions and didn't get good answers, and they jumped straight to having me start writing code. The lesson here is: you really have to hold your ground under pressure and make sure you fully understand the problem before you start writing code.

Round 3. Two engineers from other teams asked an hour of behavioral questions.

Round 4. An engineer from yet another team grilled me with another hour of behavioral questions (I also discovered I really can talk).

Wrap up — the recruiter came in to talk about compensation, status, and relocation.

Two days later, the recruiter emailed me to tell me I didn't get it.