Your question is Ship Backward-Compatible Mobile Features. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
You are preparing to ship a new mobile feature to a large installed base where many users stay on older app versions for weeks or months. The feature depends on new client behavior, but your backend and product experience still need to work for users who have not updated yet.
How do you think about backward compatibility when shipping mobile features to a large installed base?