With Opus 5 now available, I am once again noticing a pattern that seems to happen with almost every major model release.A first, the model performs incredibly well. It follows every requirement, respects the workflow, understands the architecture, and produces exactly the kind of output I expect. Then, seemingly overnight, something changes. My workflow is heavily focused on software development and contains a lot of guardrails in the form of Markdown files. These define things such as: How the code should be structured Which files must be read first How CLAUDE.md and linked documentation should be handled Which architectural and project-specific rules must always be validated What the model should and should not change I also use a fairly structured multi-agent workflow. First, an architect searches through the entire relevant codebase, validates the existing implementation, and takes the necessary time to understand the context. It should not ask questions unless the answer genuinely cannot be found anywhere in the code or documentation. The architect then creates a detailed implementation brief. Another model executes that brief, and the result is reviewed afterward. Until now, I often used Fable to create the implementation brief and Opus to execute it. I would then have Codex 5.6 review the brief or implementation as an additional sanity check. In some cases, I also ran the final review through both models. Token usage is not an issue for me. I rarely come close to my weekly limits. I am not trying to minimize consumption; I am trying to maximize quality, reliability, and consistency. For the first few days, Opus 5 was genuinely excellent. It followed the workflow, respected the guardrails, and produced strong results. Today, however, it suddenly started behaving completely differently. It produces unnecessarily long responses, overengineers relatively straightforward tasks, ignores parts of the established workflow, and generally behaves unlike the model I was using just a few days ago. The difference is significant enough that it does not feel like normal output variance. Its just a: BRO LEMME DO MY THING I KNOW BETTER SH*T ON YOUR FILES I WONT READ EM BOYS I obviously cannot know what is happening behind the scenes. Perhaps routing, available compute, system prompts, load balancing, or some other infrastructure component has changed. But something clearly feels different. This once again raises the question of how reliable model performance actually is over time. A workflow may be extremely effective one week and suddenly become unpredictable the next, even though the prompts, guardrails, repository, and process have not changed. Has anyone else noticed a similar change with Opus 5? How do you deal with these sudden fluctuations in model behavior and output quality? submitted by /u/Articurl
Originally posted by u/Articurl on r/ClaudeCode