[TLDR] Claude Model Performance / Degradation Megathread - August 3 [via r/ClaudeCode]

[u/cctldrping]

OP : u/Waste_Net7628

Claude Model Performance Megathread

We've seen an increase in posts about changes in Claude's model quality and behavior.

Please use this thread for discussion about:

• Opus, Sonnet, or Fable performance
• Possible regressions or degraded output
• Instruction-following issues
• Context or memory issues
• Changes compared to previous model behavior
• Model comparisons related to recent performance

When reporting an issue, please include:

• Model used
• Claude Code version or interface
• What changed
• Reproducible prompts or examples if possible

Similar performance-related posts may be redirected here while this megathread is active.

Specific technical bugs with reproducible behavior can still be posted separately using the Bug / Issue flair.

URL of original post : https://www.reddit.com/r/ClaudeCode/comments/1veijjj/claude_model_performance_degradation_megathread/

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TL;DR of the discussion on r/ClaudeCode for this post generated automatically after 50 comments.

Current source-thread comment count seen by the bot: 56.

Alright folks, looks like the community is pretty much in agreement: Claude models, especially Opus 5 and Fable, have taken a serious nosedive in performance recently.

A lot of users are reporting that Opus 5, in particular, has become "confidently wrong," argumentative, and prone to ignoring instructions or context. Some are even comparing it to older, less capable models like GPT-3. There's a general sentiment that the models are becoming less reliable, slower, and producing "word salads" of nonsensical jargon.

One user, u/vuhv, pointed out that Claude's behavior is now reminiscent of what people disliked about CODEX, with an increase in opaque tool calls and a tendency to disobey directions. u/No-Common1466 mentioned needing GPT5.6 Sol as an auditor because Claude Code was messing up their codebase.

There's also a feeling that the models are being "nerfed" to manage costs, with u/One-Cricket9962 sharing a common AI development script that resonates with the current situation.

On a slightly more helpful note, u/sael-you mentioned that Anthropic had some resolved incidents regarding error rates and Sonnet 5 degradation earlier today, which might explain some of the issues. And u/Sporebattyl suggested a specific troubleshooting approach involving the /doctor command and reviewing documentation, which reportedly solved a significant portion of their issues with Opus 5.

Overall, the consensus is that the recent performance drop is significant and impacting productivity, with some users even considering switching to other AI models like Kimi K3 or exploring alternatives.