Your Prompts Have a Version Number
A prompt is written for a particular model, even when the file never mentions which one. Change the model and you may change what that prompt does.
Anthropic’s prompting guide includes model-specific guidance and migration advice. It’s worth reading that kind of documentation before carrying old prompts into a new release.
Old prompts carry old scar tissue
Production prompts accumulate workarounds. An ALL-CAPS instruction the old model kept ignoring. A prefilled response to force a format. Three examples added after a specific failure in March.
Those choices may have been useful at the time. They still need review when the model changes. A workaround can become redundant, conflict with a new instruction, or depend on an API feature the replacement model doesn’t support.
Anthropic suggests a useful clarity check: ask a colleague with little context to follow the prompt. If they struggle to understand it, revise the instructions before adding more workarounds.
Keep the prompt with the code
I treat prompts as maintained parts of the application. They belong in version control, with a record of the model and settings they were tested against. A model upgrade goes through the same evaluation process as other changes to the system.
The migration checklist is short:
- Read the vendor’s notes for the model you’re moving to.
- Review existing workarounds and remove the ones that are no longer needed.
- Run the evaluation cases against the old and new configurations. Inspect failures as well as the overall score.
- Release the model and prompt changes together, keeping the previous versions available for rollback.
Save the evaluation results with the change. The next person editing the prompt should be able to see why an instruction exists and what happened when you changed it.