The entire timeline is complaining that Sonnet and Opus 5 are dumb. I don't blame them. Sonnet 5 and Opus 5 are dumb out of the box. Fix a few things, and they instantly feel 10x smarter. Thank me later (advice straight from Anthropic: 1. Stop porting over old prompts Skills and system prompts built for older Claude models can actually make Claude 5 worse, not better. Anthropic says to start fresh instead of reusing what worked for Sonnet/Opus 4.6 or older. 2. Stop telling Opus 5 to "double-check itself" It already catches and fixes its own mistakes without being asked. Adding "verify your answer" just stacks on top of what it's already doing and burns tokens for nothing. 3. Ask for brevity directly Opus 5's default answers run longer than previous versions. Effort level doesn't shorten responses on its own. Say exactly what you want: "keep this concise, skip the caveats, get to the point." 4. Constrain scope explicitly Opus 5 will expand a task on its own if you're vague, adding steps you didn't ask for. Be specific about exactly what you want it to do and tell it to stay on target. This is the biggest tip I can give you 👆 5. For review work, ask for everything first, then filter If you tell Opus 5 to "only flag serious issues," it takes you literally and under-reports. Real problems slip through. Ask for full coverage first, then filter in a second pass. 6. Raise the effort level for Sonnet 5 Sonnet 5 respects effort settings strictly. On low/medium, it scopes exactly to what was asked, which means genuinely complex problems get shallow reasoning back. Default it to xHigh, trust me. 7. Give Sonnet 5 a concrete spec for design work On frontend briefs, Sonnet 5 settles into one fixed house style. Highly recommend using a dedicated design skill; otherwise, Sonnet 5 is just horrible at design. 8. Say exactly what you mean These models are extremely literal now. Claude 5 does exactly what you ask, so be very specific with what you need and, if needed, tell Opus not to wander off. Just copy/paste this tweet into a Claude chat, and it can create a checklist for you to follow when prompting Claude 5 models. Hope this helps!(Miles Deutscher)