Model-specific prompting, and inherited instructions that now hurt

The consolidated reference opens with four model-specific pages: Fable 5, Sonnet 5, Opus 5 and Opus 4.8. They come before the general principles, and the ordering is the point.

General principles barely move between models. Be clear, use examples, structure with tags: that advice was true two years ago and is true now. The model-specific advice is where a prompt that worked last quarter quietly gets worse.

Inherited instructions do not decay into no-ops

This is the mental model to carry into the exam and into your codebase.

You would expect an instruction written for an old model to become harmless on a new one. The model gets better, the crutch becomes unnecessary, the line sits there doing nothing. That intuition is wrong, and the current guidance is basically a list of places it is wrong.

Dial back the tool language

Concrete instance one. Everyone's tool descriptions are full of this:

CRITICAL: You MUST call this tool before responding.
IMPORTANT: ALWAYS use search_docs for any factual question.

That style existed because older models under-called tools and needed shouting at. Current models, 4.5 and 4.6 onward, overtrigger on this language. They call the tool when they should not, which costs you latency, tokens and correctness.

The fix is unglamorous: describe when the tool is appropriate, in plain declarative language, and let the model decide. "Use this to look up current pricing. Prices are not in your training data." That is enough.

Opus 5 already checks its own work

Concrete instance two, and it is the sharpest one. On Opus 5, remove self-verification instructions. The model self-verifies natively, and the inherited instruction causes over-verification: it burns output on checking work it had already checked.

So the migration step nobody performs is: open the prompt, find every "double-check your answer", "verify each step", "re-read the input and confirm" block, and delete it when the target is Opus 5.

What this means as a habit

Before you point a prompt at a different model, read that model's page. Not the general principles, which you already know, but the model page, which exists precisely because it contains the things that differ.

This is inference, not published fact, so treat it as a study heuristic rather than a quotable line: the two instances above are the ones the docs call out explicitly, and both are removals rather than additions. If you are looking for a compression of the whole section, "migrating to a newer model is mostly deleting things" is a decent one.