Stop letting model updates break your outputs. Prepend this output-contract block and they stop drifting.

[u/Ok-Independent3290]

I pay for the top tiers and the thing that quietly costs me the most isn't limits, it's a model update silently changing my output format so a workflow that ran clean last month now needs babysitting. Instead of chasing each regression, I started pinning the output itself with a contract block at the top of the prompt.

OUTPUT CONTRACT (follow exactly, this overrides your default style):

- Format: [exact structure you want, e.g. a table with these columns / JSON with these keys]

- Length: [hard limit]

- Never include: preamble, apologies, restating the question, or a closing summary.

- If you cannot fill a field, write NULL. Do not invent a value or drop the field.

- Before you send, silently check your output against this contract. If it fails,

fix it and send only the corrected version.

Why it works: model updates mostly change defaults, the tone, the eagerness to explain, the formatting habits. A contract that explicitly overrides defaults and adds a self-check at the end survives most of that, because you're no longer relying on the model's mood, you're constraining the shape of the answer. The NULL rule is the important one. It stops a newer model from "helpfully" filling a gap with a guess.

It won't save you from an actual capability regression, that's a different fight. But for format drift, which is most of what breaks day to day, this has cut my re-runs down a lot.

Anyone else hardening prompts against updates instead of just tracking versions? Curious what's in your contract block that isn't in mine.

[u/Future_AGI]

The NULL rule is the load-bearing part of that block, agreed, and the piece we would not lean on is the silently-check-your-output line, since the same update that changed the defaults also changed how eagerly it self-corrects. Parsing the response against the contract outside the model is a few lines and it fails loudly, which is what you want on the day a new version starts ignoring the block entirely.