A team is migrating from claude-3-sonnet-20240229 to claude-3-5-sonnet-20241022. During regression testing, they discover that 8% of previously passing test cases now produce different outputs — not wrong outputs, just different phrasing or structure. The PM wants to declare the migration failed due to behavioral change. How should the architect respond?

B is correct because different does not mean wrong. Model version upgrades routinely produce phrasing, formatting, and structure variations that are functionally equivalent — a sentence reordered, a bullet converted to prose, a synonym substituted. These are not regressions in any meaningful sense. The correct migration quality gate is functional correctness: are the outputs factually accurate, safety-compliant, and parseable by downstream systems? Auditing the 8% to separate stylistic divergence from functional regressions allows the migration to proceed on the correct evidence basis, and documenting acceptance criteria makes future migrations more rigorous. A is wrong because requiring identical outputs between model versions is an unrealistic and counterproductive standard — it would prevent any model version upgrade forever, and newer models are typically more capable, not less. C is wrong because averaging across runs addresses variability within a model version, not the behavioral differences between two different model versions — this approach misdiagnoses the problem. D is wrong because split-version deployment creates a maintenance burden of running two model versions indefinitely and introduces its own complexity — it should not be the standard migration strategy for stylistic divergence.