I applied online. The process took two weeks.
A recruiter call was followed by a System Design Interview disguised as a coding interview with two engineers. The interview was delayed by ten minutes because the main interviewer went AWOL, but it still ended on time, which honestly was a bit unfair.
They presented the interview using a collaborative coding pad, but there was really no coding involved, so don't stress about what data structure to use in your class. Make sure you go breadth-first by drafting out all endpoints that meet the list of requirements before diving deep into each of them.
For the tiny URL service, just go read chapter 8 of the book System Design Interview.
The following metrics were computed from 7 interview experiences for the WHOOP Senior Software Engineer role.
WHOOP's interview process for their Senior Software Engineer roles is extremely selective, failing the vast majority of engineers.
Candidates reported having mixed feelings for WHOOP's Senior Software Engineer interview process.