Background: I'm a C++ dev with 30+ years experience, ex-FAANG Staff Engineer. I'm generally the person on the team that other developers come to after they struggled with a problem for a week, and I would solve it while they are standing in my office.

But today I was humbled by Claude Opus 4.

I gave it my white whale bug which arose from a re-architecting refactor that was done 4 years ago. The original refactor span around 60k lines of code and it fixed a whole slew of problems but it created a problem in an edge case when a particular shader was used in a particular way. It used to work, then we rearchitected and refactored, and it no longer worked.

I've been playing on and off trying to find it, and must have spent 200 hours on it over the last few years. It's one of those issues that are very annoying but not important enough to drop everything to investigate.

I worked with Claude Code running Opus for a couple of hours - I gave it access to the old code as well as the new code, and told it to go find out how this was broken in the refactor. And it found it. Turns out that the reason it worked in the old code was merely by coincidence of the old architecture, and when we changed the architecture that coincidence wasn't taken into account. So this wasn't merely an introduced logic bug, it found that the changed architecture design didn't accommodate this old edge case.

This took a total of around 30 prompts and one restart. I've also previously tried GPT 4.1, Gemini 2.5 and Claude 3.7 and neither of them could make any progress whatsoever. But Opus 4 finally found it.

Latest Performance and Bugs with Workarounds Report: https://www.reddit.com/r/ClaudeAI/wiki/latestworkaroundreport

Full record of past Megathreads and Reports : https://www.reddit.com/r/ClaudeAI/wiki/megathreads/

Why a Performance and Bugs Discussion Megathread?

This Megathread should make it easier for everyone to see what others are experiencing at any time by collecting all experiences. Most importantly, this will allow the subreddit to provide you a comprehensive periodic AI-generated summary report of all performance issues and experiences, maximally informative to everybody. See the previous period's performance and workarounds report here https://www.reddit.com/r/ClaudeAI/wiki/latestworkaroundreport

It will also free up space on the main feed to make more visible the interesting insights and constructions of those using Claude productively.

What Can I Post on this Megathread?

Use this thread to voice all your experiences (positive and negative) as well as observations regarding the current performance of Claude. This includes any discussion, questions, experiences and speculations of quota, limits, context window size, downtime, price, subscription issues, general gripes, why you are quitting, Anthropic's motives, and comparative performance with other competitors.

So What are the Rules For Contributing Here?

All the same as for the main feed (especially keep the discussion on the technology)

• Give evidence of your performance issues and experiences wherever relevant. Include prompts and responses, platform you used, time it occurred. In other words, be helpful to others.

• The AI performance analysis will ignore comments that don't appear credible to it or are too vague.

• All other subreddit rules apply.

Do I Have to Post All Performance Issues Here and Not in the Main Feed?

Yes. This helps us track performance issues, workarounds and sentiment and keeps the feed free from event-related post floods.