The interview process was incredibly long. I interviewed for two months for the position, and did 3 rounds of hour long interviews plus a technical test which took about 5-6 hours total.
First interview is with one of their recruiters, where they discuss your general experience and motivations for joining Adyen, and whether you are a fit for the role. If you pass this, you have a take home assessment to do before you can be offered a second interview.
The 2nd interview is a technical skills interview with two members of the team, where they ask you about the technical assessment, and discuss at length your motivations for joining Adyen.
If you pass the technical interview, you have a 3rd interview with two team leads, which is completely identical to the previous interview, so be prepared to repeat yourself a lot with this company as they do not seem to retain any information you have provided in previous interviews.
After this round of interviews, I was told I was a great fit for the role, I fit well with the team and my technical skills and experience were great, but that they were rejecting me due to the fact I did not show enough excitement for Adyen as a company during the 3rd interview. It took quite some back and forth before they told me over email that they were actually looking at other candidates with more experience, so be prepared to do some digging to get some honest feedback.
Generally quite a negative interview experience, as it took 2 months and a large chunk of my time and energy only to be rejected for a reason that they could have easily ascertained during the first interview.