I heard back from them a month after applying.

The first step is an online C/C++ quiz where you look at snippets of code and try to determine if there is a problem (off by one, infinite loops, etc.) or if the code is good.

After that, you get a phone interview from someone who is likely not a programmer. They have a list of questions and want to hear a 2-sentence answer to write down. This person is not interested in hearing examples or thought processes; it's essentially a pop quiz that gets passed to an engineer afterward for grading. Unfortunately, this method provides little to no feedback. During other interviews with companies, I would be talking to an engineer, and so if I struggled a bit, we would work through it together. Here, you'll just get stuck and likely fail.

If you pass that, which I didn't, the next step is a 1-hour phone interview with an engineer.

After that, a 6-hour coding challenge in a screensharing environment so that an engineer can watch you code. This is presumably so that you can't blatantly copy and paste stuff from GitHub or Stack Overflow.

Then there's the onsite interview.

List all of the sorting algorithms you know and their complexities.

What is a pure virtual function?

What are the 4 types of C++ casts?