C3 is a company that has changed its focus (and name) several time over the years, from C3 Energy, to IoT, and finally now AI. Their business model relies on winning tech contracts (similar to Palantir), and building up customised SaaS apps which allows companies to leverage their data. In the Applications group, you don't implement models (that's done by data scientists), work on the core components that run or visualize the data (that's under Platform), or with clients (which is done by FDEs), but rather sit in the middle and build on top of the internal platform, which makes it difficult to acquire transferable skills and take ownership. The people in leadership positions seem to have been there a long time, which tells me it's not necessarily a great place to advance your career.
Rounds included an online coding challenge, then a technical screen with an engineer, then a technical onsite with three engineers (2 engineers and a technical lead), and finally talking to Director of Engineering and VP of Applications. All interviews were conducted in Microsoft Teams. The process took 5+ weeks, and I had to reach out to the recruiter every time to get the next round scheduled.
I would describe the interviewers as lukewarm/having a lack of enthusiasm, and considering I made it to the end, I'm a little surprised I didn't get the offer. To give them props, they moved their decision forward when I told them I had a competing offer. It's not an environment for everyone, be prepared to move projects often and get through tickets quickly, but if you can adapt to the culture it seems like it pays well.