Just wrapped up my loop at Loom (senior SWE, L5-equivalent). Posting because I couldn't find much specific info before I went in.
System design was 60 minutes with two engineers. They gave me a prompt that was essentially: design a video recording and sharing platform. Which, yeah, they use internally as a reference but they're not going to tell you "design Loom." The framing was more abstract, something like design a system to capture, store, and deliver short video clips at scale.
What mattered: They pushed hard on the storage layer. CDN choice, chunked upload, handling large files. They wanted to hear you think through blob storage vs. a managed video service. Latency questions came up fast. How do you make playback feel instant? Adaptive bitrate, preloading segments, what do you do when the viewer is on a slow connection. They asked about the notification / link-sharing side too. How do you generate a shareable link, track views, handle access control. This surprised me a little, I expected to stay on the infra side longer. One of the interviewers specifically asked how you'd handle the recording client losing connection mid-upload. Error recovery, partial uploads, resumable uploads. That got a bit deep.
The interviewers were genuinely engaged, not just waiting for you to hit the "right" answer. They pushed on tradeoffs rather than fishing for a specific solution.
Timing felt tight. 60 minutes goes fast when you're covering upload pipeline, storage, CDN, access control, and edge cases. I'd practice keeping your initial architecture pass to 15-20 minutes so there's room to dig.
No particular emphasis on specific cloud providers. AWS/GCP both came up in my answer and no one flinched either way.
Overall I'd say it's a solid system design round. Not a gotcha, but not easy either. The video domain adds interesting wrinkles that a generic "design Twitter" prep won't fully cover.