Went through this recently for a senior SWE role on the Autopilot software side. Let me just give you the actual format because there's almost nothing accurate out there.
Online assessment (OA) stage: They use HackerRank. Two coding problems, 90 minutes. In my batch it was one medium and one medium-hard by LC difficulty. No system design in the OA. One problem was a graph traversal problem (BFS/DFS, pretty standard), the other involved some array manipulation with a constraint that made brute force O(n^2) and required a sliding window or heap approach.
That's it. No behavioral questions in the OA. Some people report a third problem but I didn't see one.
Technical phone screen (if they do one): Not everyone gets this step. Mine was skipped and I went straight to onsite. When it does happen, it's 45-60 minutes, one LeetCode-style problem, usually medium difficulty. The recruiter will tell you the format when they schedule it.
Onsite coding rounds: Two coding rounds, 60 minutes each. Both used a shared coding environment (not HackerRank, just a Google Doc or CoderPad depending on the team). One was a straightforward medium problem where the main test was handling edge cases clearly. The second was harder, closer to a hard but with a scaffolded start: they gave me the skeleton and wanted me to fill it in with a specific algorithmic approach.
A few notes: They do care about clean code and clear naming, not just a working solution. One interviewer explicitly said "pretend this is a code review." Verbalize your thinking before you type. They interrupt if you go silent too long. C++ is fine. Python is fine. They do a lot of C++ internally (Autopilot is C++ heavy) but they don't require it for SWE interviews unless the JD says so.
Overall difficulty: medium-heavy for senior. Not "grind 300 leetcode hards" hard, more like "be solid on core data structures and know when to ask clarifying questions."