Did the Linear coding round earlier this year for a mid/senior backend role. Here's what actually happened, because the info online is sparse.
There was no automated online assessment for me. No HackerRank, no Codility. I was invited directly to a 60-minute live coding session with an engineer.
Format. One problem, in a shared editor (they used their own internal tool, it was basically a Monaco editor with chat). Language was my choice; I used TypeScript which felt on-brand for them. Problem statement was shared in the chat.
Difficulty. Somewhere between LeetCode medium and hard, but not in the typical "graph traversal" sense. It was more of a real-world-ish data manipulation problem. Think: you have some structured input that looks like it could be project data, write something that transforms it. Not a trick problem. But the edge cases mattered and they asked me to handle them incrementally.
What they watched. They watched how I broke the problem down before writing any code. I probably spent 8-10 minutes talking through my approach and asking clarifying questions. They engaged with that, asked a few "what if the input has X" questions. Didn't feel like they were trying to catch me; felt like they were curious how I think.
Optimization. After I had a working solution, they asked about time/space complexity and then asked if I could improve it. The improvement was non-trivial (involved restructuring the data) but not exotic.
Overall difficulty. Honestly more accessible than big-N if you've done any real coding recently. But it's not a "grind 200 leetcode" type of prep. You need to be genuinely comfortable writing clean code live under light pressure.
One thing I'd flag: they noticed when I wrote something overly clever or unclear. The interviewer asked me to rename a variable at one point. Take that as a signal about their culture.