I applied through an online hiring challenge, after which I got a call from the HR for the remaining interview process which was conducted in their office. The first round was the programming round where the solution is basically judged on the design and scalability. This is followed by pair programming where a Thoughtworker sits with you to refactor your solution (Great learning experience). Next two rounds are technical rounds where the ThoughtWorkers discuss about your projects (be thorough with them), they ask you to design algorithms on the white board.
If you clear this, you are as good as selected but there are few more rounds like the flow chart round, English/Maths ability, HR round and Values round