How would you answer an interview scenario involving backward-compatible API changes?

In an interview, I would first define backward-compatible API changes and the problem it solves, then explain how I would prefer additive changes, preserve defaults, tolerate old request shapes during migration, use contract tests, and verify real consumer behavior before removing compatibility code. I would also call out the main failure mode: assuming clients ignore unknown behavior or can instantly adopt a renamed field often causes production breakage across independently deployed consumers. Finally, I would describe how I would test, monitor, and safely roll back or recover the solution.