Lengthy interview process took place over nearly two months, with 6 rounds in total, covering a broad range of technical and non-technical topics with a take home coding test and an in-person system design interview. At all stages it felt like they were really drilling deep on what my specific contribution to each project I'd worked on was, including how I used data to back up any decisions. The take home coding test took a while, and then I didn't actually get many questions about it but I think it's because I'd covered off most of what they might ask about.
I received very detailed feedback which was really appreciated, and the hiring manager was very communicative. I had a mix of positive and negative feedback, with some of the negative feedback from one of the in-person interviews seeming slightly harsh and at odds with how I felt the interview went, but for the most part it was fair.
I felt the process was too long and I was stalling other offers whilst waiting for my last round.
Overall the interview process was very in-depth and I definitely got the feeling Checkout have high expectations for the Staff Engineer role, so I'd recommend good preparation, especially around being able to explain the details of previous projects.