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Retiring Your Favourite Prompt When The Model Changes Underneath It

By Nigel Guy · 2 min read

Most people find a prompt that works well and then keep using the exact same wording indefinitely, treating it as a fixed asset rather than something tuned to a particular model at a particular moment. That's a reasonable habit right up until the model underneath it changes — a new version, a provider switch, a quiet update you weren't told about — and the same wording starts producing something subtly different. The prompt doesn't announce that it's gone stale. It just quietly stops working as well as it used to.

The mechanism: the re-certification check

1. Note which model a favourite prompt was tuned against, if you can. Exact model names and version numbers change fast enough, and are labelled inconsistently enough across products, that this is worth double-checking rather than trusting memory — check the current documentation for what you're actually running before you assume.
2. When you know or suspect the underlying model has changed, rerun the prompt on a case where you already know what a good answer looks like. A past real example works better here than a fresh one, because you have something concrete to compare against.
3. Compare the new output against that known-good benchmark, not just against "does this look fine on its own." Wording that once compensated for an older model's specific quirk may now be redundant, or actively working against a model that no longer has that quirk.
4. If the output has genuinely drifted, retune the prompt as if it were new — don't assume a single word swap restores it. Treat it as a fresh round of testing, not a patch.
5. Retire any language that was clearly a workaround for a limitation the current model doesn't seem to have any more. Carrying old workarounds forward is harmless at best and actively confusing at worst.

What to skip

Skip re-testing every prompt after every minor update — reserve this for prompts that actually matter: recurring reports, anything client-facing, anything used often enough that drift would compound. Skip assuming a favourite prompt is broken just because its output looks different from before — different isn't automatically worse. Check it against the benchmark before you start retuning something that wasn't actually broken.

Guardrails

• Exactly when and how often the underlying model changes isn't something to state as settled fact here — it varies by provider and product, and changes often enough that it's worth checking current release notes rather than assuming a fixed schedule.
• You won't always be told when a model has changed underneath a product you use day to day. A periodic scheduled check on your important prompts is more reliable than waiting to notice something feels off.
• This is about catching output-quality drift in prompts you rely on. It's not a substitute for actually reading a provider's release notes when they publish one — those will tell you more precisely what changed than a benchmark comparison can infer on its own.

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