just finished the coinbase OA and wanted to write this up while it's fresh because i couldn't find anything recent when i was prepping.
for new grad / entry-level: it was a hackerrank assessment, 90 minutes, 2 problems. the first was medium difficulty by leetcode standards -- graph traversal, finding shortest path with some constraints. not a standard dijkstra, but close enough that knowing BFS/DFS well would get you there. the second was harder. it involved interval merging with a twist. i solved the first in about 30 minutes, spent the rest on the second, and got a partial solution that passed maybe 60% of test cases.
i advanced to the next round, so partial credit is real. don't panic-abandon a hard problem. partial passes matter.
for the senior loop, a friend who went through it around the same time said the coding portion was 2 rounds, each 45 minutes, with one interviewer per round. he said the difficulty was medium-hard. one was a string manipulation problem that could be done with a sliding window, one was more of a design-adjacent coding problem (implement a rate limiter class with specific behavior). so they're not just testing pure algorithm knowledge, they want to see you think about APIs and edge cases.
prep advice based on what i've seen: medium array/string problems on leetcode are the floor, not the ceiling know your sliding window, two pointers, basic graph traversal cold for senior: they'll ask you to think about edge cases aloud before you start coding. don't skip that write clean code even in interviews. variable names matter to them apparently
timing for the OA: i got it 4 days after the recruiter screen. had a 7-day window to complete it. i took it on day 3.