Your provider is deprecating the model you built on. How do you detect and measure regression before migrating?
Model migrations break things that benchmarks never show, format quirks, refusal shifts, tool-calling drift. The eval-replay and shadow-traffic playbook for migrating without surprises.
Updated Aug 2026 · Grounded in real Forward Deployed Engineer interview loops and written to a senior-engineer editorial bar.
Model migrations break things that benchmarks never show, format quirks, refusal shifts, tool-calling drift. The eval-replay and shadow-traffic playbook for migrating without surprises.
Lead with where the obvious approach breaks, because that is the judgment they are screening for — most candidates jump straight to the happy path and lose the room.
Then walk the failure back through the pipeline in order, naming the one metric the customer's exec sponsor actually cares about before you propose the fix.
