How do you write prompts that survive model upgrades?

Write specifications, not incantations: clear role, task, examples, and structured output transfer across model versions, whereas persuasion hacks ('you are the world's best…') are artifacts of one checkpoint. Pin the model version in production and treat upgrades as deliberate changes: branch, run an evaluation suite (a golden set of real cases), compare quality, cost, and latency, then promote. Keep prompts in version control tagged to the outputs they produced so you can diagnose regressions.