I came in pre-vetted by a third party, which allowed me to skip some of the initial steps. I interviewed at their SF office (which has a gorgeous view of the Bay, BTW) for a machine learning role.
People were friendly and I was impressed by how seamless remote meetings with people from other offices were. I'm glad to see Niantic embracing inter-office mobility, since I actually preferred the location of a different office and it wasn't a problem with them.
The interview process itself consisted of a few 1 hour technical and nontechnical talks with supervisors and senior engineers from the team I'd be interviewing with. I was interviewing for a role on the machine learning side of the engineering team, so many of my questions were ML challenges. These were easy to moderate challenges, involving some basic stat knowledge and a few simple classifiers (no deep learning or computer vision challenges). One question required me to recall Bayes' theorem from memory (which I was thankfully still able to do), when it probably would have been more reflective of a real world work environment to allow me to look up whatever I was hazy on and test me on the use of it.
They notified me that the interview went very well, and the next step would be (nontechnical) chats with the CTO and CEO. Both are pretty busy people, so these took a few days to schedule. I really enjoyed these; their execs have a compelling vision and they were able to pitch it very effectively.
I was told I'd be getting an offer, but at this point the process stalled for a couple of weeks. It came in just as I was about to accept an exploding offer from another company, and was extremely competitive. The sales pitch on the offer was straightforward and low-pressure, which I appreciated. The offer was contingent on three reference checks and a background check, but these thankfully weren't an issue so much as an additional delay.
I think they have opportunities to streamline the offer process, but overall I'm very positive on the company!