claude-code - 💡(How to fix) Fix Opus 4.6 reasoning regression: fails simple file access tasks that Haiku handles correctly [3 comments, 3 participants]

When a file exists at a known absolute path and the model has full filesystem access, Opus 4.6 diagnosed the situation as a "tooling limitation" rather than simply reading the file. It produced multi-step diagnostic frameworks, offered "fix options," and explained why the file was inaccessible — without ever attempting to read it.

TL;DR

The most likely fix for Opus 4.6's reasoning regression is to modify its decision-making process to attempt file access before diagnosing tooling limitations.

Guidance

• Review the Opus 4.6 code to identify where it checks for tooling limitations and file accessibility, and consider reordering these checks to prioritize actual access attempts.
• Verify that the model's Read tool is correctly configured and functional by testing it in isolation.
• Compare the decision-making logic between Opus 4.6 and simpler models like Haiku to identify potential differences that could be contributing to the regression.
• Consider adding logging or debugging statements to track the model's thought process and identify where it's going wrong.

Example

No code snippet is provided due to lack of specific implementation details in the issue.

Notes

The exact cause of the regression is unclear, and further investigation is needed to determine the root cause. The suggested fix is based on the observed behavior and may not be comprehensive.

Recommendation

Apply a workaround by modifying the Opus 4.6 decision-making process to prioritize file access attempts, as this is likely to improve the model's performance on straightforward tool-use tasks.