model migration

Benchmark gains do not cover what users built around the old model. Measure the behaviour that changed, give people a bridge and decide in advance when the old model goes.

A puzzle with a precise answer. Price per token is only comparable if a token means the same thing, and across model generations it often does not.

A deadline you did not choose and a change that touches every output. The interviewer wants a plan that treats API compatibility and behavioural compatibility as different problems.