Seemingly three stages, though it is possible there are more stages given a candidate is successful on the third stage: a phone interview with a technical sourcer, a phone interview with an existing Systems Reliability Engineer (SRE), and then an onsite interview in Durham, NC with 2 SREs and a WW Support Manager. My only complaint throughout the entire experience was how awful the actual Durham location seems to be, but maybe I missed something obvious about ease of parking and to be honest I didn't get much time to actually explore the surrounding area. On the bright side, the people seem great!
The initial phone interview with HR basically went through some basic information about the role while asking a few questions about familiarity in some aspects of the role. The second phone interview had the SRE further diving into the role, speaking about their experience at Nutanix, and mentioning a few key tasks that they hope interns to regularly partake in. The onsite interview consisted of a run-through of four pillars - networking, virtualization, storage, and Linux. My knowledge outside of networking and virtualization is pretty lackluster, with my knowledge of networking and virtualization to begin with not being anything incredible, so I think that's where I fell short during the onsite interview. I don't remember specific questions that were asked, but the gist of it seemed to be fairly fundamental TCP/IP, virtualization experience with Hyper-V and VMWare since those were the two hypervisors I had used, software-defined storage (I assume) if applicable, and Linux questions ranging anywhere from the strengths of Linux to basic Linux commands.
Despite the rejection, arguably the most solid interviewing experience I had in the past two years of interviewing on and off while holding a job! HR made things painless, the onsite interview folks seemed great, and everything seemed 100% fair! Kudos!