Opus 5 changed one thing that nobody documented: it assumes instead of asking. 4.8 would stop and clarify when my prompt was underspecified. 5 fills the gap itself, picks a direction, and starts building. By the time I read the first tool call it has already committed to an approach I didn’t want. It also writes tests I never asked for, mid-task, which is where a lot of the token burn comes from. This isn’t the model being worse. It’s the model being more willing to act on an incomplete spec. Which means the fix isn’t a better prompt, it’s giving it the constraints before it has a chance to invent them. Here’s the new thing I paste at the top of a session now ⬇️ Before writing any code:
- If the task is underspecified, ask me. Do not choose for me.
- State your approach in 2-3 lines and wait for me to confirm.
- Do not write tests unless I ask for tests.
- Do not refactor anything outside the files I named.
- If you hit a decision with more than one reasonable answer, stop and ask. Only five lines. The behavior change is immediate and it holds for the rest of the session. The part that surprised me: the “state your approach and wait” line does more work than the other four combined. Opus 5 will happily plan out loud if you tell it to - it just won’t do it on its own, because its default now is that momentum is more helpful than a question. If you’ve been feeling like 5 is worse than 4.8, try this before you roll back. In my experience it isn’t a worse model, it’s a model that stopped asking permission, and it gives the permission back the moment you ask for it. What are you all putting in yours to improve Opus version 5? submitted by /u/aiblastoff
Originally posted by u/aiblastoff on r/ClaudeCode
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