It all took about 5 weeks for the interview process (all of it online) but another 3 weeks for the to come to a decision.
It was first a 30 min interview with someone from the banking team with relatively basic question on how TransferWise works and on fit: whether you have a large bank mindset or a startup mindset.
The second interview was with the hiring manager for about an hour and then you had to solve a case for an hour. The interview delved a little deeper on regulatory and industry knowledge. The case itself was simple: pitching TransferWise to a bank doing a few numbers in excel with some support material.
Then there was a third interview with the head of Banking which again delved into regulatory and industry knowledge as well as behavioural questions.
Lastly, there was the founder interview with on other than the CEO himself Kristo Kaarmann. This was the hardest one. There is even some material online about his interviews written by himself, but honestly that did not help me much. He'll always try to dig deep and ask "why?" over and over again basically. He comes off a bit arrogant and unpleasant but I had been warned before. I had the opportunity to meet him a few months after the process and he is very different outside of the interview process, keep that in mind so you don't go running the other way when interviewed by him.
Overall great process. The recruiters I had the pleasure of working with were the best I've ever encountered (shout-out to Jana and Eltje!). The interviews were insightful. I did not get the job in the end as they chose another candidate. They only thing I would have liked a bit more of is feedback from the interviewers.