I had an interview with Karat, it was nice: very fast and professional. Only thing that was slightly frustrating at the time was that you guys insist on completely correct solutions. Also, the behavioral part at the beginning felt kind of forced.
There are no behavioural questions, the intro bit at the start is just there to not abruptly start asking questions, help you relax a bit, and also nice in case the client wants to look at the video to find out more about you. We do insist that your code works correctly, that's true. We're not overly anal about the format of your solution, but we do expect to cover all edge cases.