Multilayered, including some offline tasks. At the last stage it gets really intense, with many 1-1s in succession. Some interviewers were very narrow in the topics they would ask about, especially the ones related to The Trade Desk core business.

BEWARE of the risks of applying here: the interview process takes supreme efforts and time, and there's a high risk of being rejected, even if you are good, and even worse: of them not giving you a single line of feedback, but a one-liner email saying they won't make an offer. I also got the feeling they mainly want free insights from candidates for the real data problems they have, but they are not currently truly hiring. They also don't care about getting to know you as a person but only putting your brain to the test. I would definitely not recommend interviewing here. Also if you are applying for a London role, the fact that the headquarters of this company are in the US means you will have to stay late - the interviewers themselves were saying how this is one of the 'biggest challenges'. The process started with a 'screening' phone call. This was a rather friendly chat so I fell for it and foolishly accepted continuing the process. After this, they sent me a 'takehome assignment', which took me about 1 week to complete after work. They gave me a dataset and several tasks to complete, including rocking up with a prediction model from scratch. Then they told me they had really liked my submission and arranged another 1 hour phone call to review it (yes, they don't even invite you onsite to discuss it as with most companies). During this call, the interviewer mainly focused on the things I didn't do or didn't get so right - which definitely doesn't make you feel too good after all the effort you put for it. They then invited me to a half-day onsite. And this is actually more than half a day - it's 3 highly technical interviews of 1.5h each (although they tell you they will take 1h each). And btw, they didn't give any useful help to prepare for this whatsoever. After all this, they then took 3 days to get back with an answer, which was a one-liner rejection, without any feedback whatsoever. I have contacted several times since then asking politely for feedback, but they have not replied back at all - not even with a reason to not provide feedback! What's worse is that I thought I had done so well actually! Now you tell me if this sounds worth of your time :)