Your feed change spreads through communities — is the A/B biased?
InterferenceHardProblem. You user-randomize a feed change, but it affects which content gets upvoted and surfaced — which changes what everyone sees. Is the A/B biased, and how would you design it?
Before you reveal: say your answer out loud, as if you were in the real interview — get your reasoning across clearly first. There is no single correct answer: reading what the interviewer is really after and defending your own thinking is what makes an answer strong.