Your nav change touches every surface — is a user-level A/B valid?
InterferenceHardProblem. You want to test a new navigation bar / information architecture. It changes Home, Search, and in-experience entry at once, and users move between surfaces. Is a standard user-level A/B valid? If not, what do you do?
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.