My interview experience lined up with the other reports on here. After a recruiter screen to confirm a little bit about my background, I did a CodeSignal assessment. I did the first two questions pretty quickly. Then I looked at the third and fourth and decided that I was better prepared for the third one. So I did that and had a few minutes to spare. I tried to do the fourth one, but I ran out of time.
The recruiter let me know I passed and then signed me up for a power day. I requested a couple weeks to prepare, since system design interviews especially were new to me. I used hellointerview and prepfully to prepare; those helped a ton.
The day of the interviews was fine. The interviewers were friendly and engaging. The behavioral and coding rounds were straightforward. Both the CodeSignal assessment and coding round were familiar from my practice of Capital One questions on leetcode. For the system design, I made detailed non-functional requirements to go with the functional ones given to me. I didn't try to do any math about SLAs or anything like that though, and the interviewer didn't ask me to. I led the conversation since that is what expected at a senior lead level.
The only one that seemed difficult was the case study interview, since it is unique to them and harder to prepare for. The question seemed bizarre, and a real-world case would need a lot more information. The instructions they give you ahead of time say not to worry too much about reality, though. The biggest advice I would give for this one is to type out your assumptions in the CodeSignal text field they give you. That will help you remember to do that and to be clear about what you are assuming about the data you are given. There may be some mental math involved -- there was for mine -- so practicing that wouldn't hurt, either. I would maybe ask an LLM to help you practice. There is a video on YouTube by Capital One about a retired case study for software engineers that they use as an example.
I got feedback the day after my power day, saying that I passed and did very well. About a week later, I had a hiring manager call that went okay, but they weren't quite what I was looking for. Then it took about 2-3 weeks for another hiring manager to be interested. This one definitely wanted to hire me, specifically referencing how well I did in the power day interviews. That came up in the compensation discussion in the call with the recruiter as well, so I would definitely prepare as much as you can, since it's a massive ROI.