Applied online, got a response about a week later that there was overlap between my skills and what they needed. Set up a phone interview with two senior designers that we had later that week.
Phone interview was a simple, if a bit contentious, portfolio review. I was surprised that they not only challenged what I said (totally fine), but did so in a pretty irascible manner. They were definitely ready for me to misspeak or screw up. Regardless, I just continued to explain my work and at the end they put me on hold for a moment and told me they'd like me to come in for an in-person session.
In-person session took place about a month later, mostly because of the Christmas break. Was a multi-part process with teams of two - I made it through three rounds, first two rounds were with two designers each and the third round was lunch with a lawyer and a developer. First round was another portfolio review, second round was a design working session (design a mobile app), third round was less focused.
What I would do differently:
First round: I spent a lot of time explaining the product I've been working on, not nearly enough time taking credit for it. I'd make sure to emphasize the scope of my role more, and to explain that I'm showing them each of these features because I was strategically responsible for them at some level.
Second round: I made a genuine mistake by jumping in too quickly to sketching out ideas on the whiteboard, without asking enough questions beforehand. Who is the target audience, Why does the client want it, basic problem discovery. In retrospect, was a pretty huge oversight.
Third round: This one was a little strange. lunch interviews with people who don't particularly want to be there are always less than fun. I was asked what I would change about Steam, which is actually a bit of a touchy topic it seems. I said that I'd try to simplify the profile/account management stuff, which is currently pretty labyrinthine, and I also said I'd want to get rid of the carousel on the homepage of the store. This received a lot of pushback, and I think I was able to defend my position well enough, but I wish I'd had more data at hand to back myself up. I also think I should have been more willing to use my anecdotal opinion of the carousel (that it's annoying and frustrating) as justification for changing it.
I was told after the third round that they weren't going to continue with me. I was given two reasons/pieces of feedback: 1. That I didn't have the strategic/high level experience necessary (this is incorrect, and effectively an indictment of my poor, overly humble self-selling), and 2. That I should have asked more questions before jumping into the working exercise (this is totally correct).
The upshot: it was an overall good experience that didn't lead to a job, but was certainly one of the more challenging interview processes I've experienced. It made me a better interviewer on both sides of the table.
My advice to future candidates: I think getting a job here as a designer takes a lot of self-positioning/selling, and a bit of luck - get them on the right day or whatever. Be aware of the product you're selling (yourself as a designer) when you go in, and sell it enthusiastically. But honestly, don't go into this one thinking you'll probably get a job. They're interviewing a LOT, have a ton of candidates at hand, and they really look for any reason to turn someone down. I don't mean this in a negative way, I just mean that you can think you're holding your own pretty well (I did), and you'll suddenly get dropped for reasons that may not make total sense to you. It's great interviewing experience at the least.