Apply online, schedule an interview at the office. When you come in, they have you sign an NDA and take away your phone. You then sit a test for an hour, it consists of a bunch of generic CS curriculum questions as well as asking to write several functions on paper. Know some generic algorithm implementations before going. Then they take you out to lunch, it's cool. Once you come back, you get your results back. If you fail, you go home, else you stay for 3-6 additional interviews. All of the interviews are technical testing your algorithmic and coding skills, though you get asked competency based questions as well. I think 1 might be a group interview but I was the only one there so they skipped this part. The questions are very similar to what you'd get asked at other interviews. I'd say it's fairly difficult, comparable to Google. After 3 interviews, you might be asked to go home, otherwise things are going alright.

During the first interview an NDA is signed, so I can't really talk in too much depth about the interview specifics. Intiially a 1-hour test is sat. The questions are very basic computer science questions, and also problem solving ones. Over lunch your test is marked, and if you've passed then you wait awkwardly while they kick out the people who didn't pass. This is supposed to be followed by a group exercise, but during my interview there were only 2 of us left out of the initial 5, and so the group exercise wasn't run. There are a number of interviews (I think I had 4) that are all technical/problem solving interviews. All the interviewers were very pleasant and friendly, and the questions weren't particularly difficult. If you pass that, then you're invited back for more interviews (pretty quickly, I think I heard within a week). The next set of interviews is largely the same - 4 more technical interviews that are very similar to the first round, maybe slightly more difficult. Then you end the day with an interview with the CTO and then CEO. Everyone was incredibly friendly and down to earth, with the CEO being especially nice. After this, I heard back within 2 working days. I noticed on previous reviews that someone suggested to not turn up over-dressed. I couldn't work out why all other candidates were so casually dressed and I was there in suit and tie, until I got home and read that review. I recommend ignoring the previous advice, and arriving dressed as you would for any other interview. Also of note is that their website is pretty sparse. They're aware of this, and don't expect you to know much about the company in advance. Everything that you need to know will be explained on the day.