Claude Opus 4.6 significant quality regression — simple tasks failing repeatedly

Preflight Checklist

• [x] I have searched existing issues for similar behavior reports
• [x] This report does NOT contain sensitive information (API keys, passwords, etc.)

Type of Behavior Issue

Claude modified files I didn't ask it to modify

What You Asked Claude to Do

Claude Code (Opus 4.6, 1M context) underperformed badly across an entire work session on 2026-04-08. Simple, well-defined tasks that should be straightforward required multiple attempts or produced unusable output.

Issues Encountered

1. Spreadsheet / Google Sheets errors

• Failed to correctly write data to Google Sheets despite clear instructions
• Required multiple correction cycles for what should be one-shot operations

1. API call failures

• Simple API calls executed incorrectly — wrong parameters, wrong endpoints, or broken logic
• Tasks that have worked reliably in past sessions suddenly failing

1. Email drafting — excessive fluff

• Asked to draft a straightforward email, received bloated, fluffy copy instead of concise professional text
• Had to repeatedly ask for rewrites to get something usable

1. Literally ask it to "by pass permissoions" w the proper command and it STILL asks me for permission.

It has clearly LOST INTELLIEGNCE

Expected Behavior
These are routine tasks Claude Code has handled correctly in previous sessions. No new complexity was introduced.

Environment

• Model: Claude Opus 4.6 (1M context)
• Platform: macOS (Darwin 22.6.0)
• CLI version: current

What Claude Actually Did

Claude Code (Opus 4.6, 1M context) underperformed badly across an entire work session on 2026-04-08. Simple, well-defined tasks that should be straightforward required multiple attempts or produced unusable output.

Issues Encountered

1. Spreadsheet / Google Sheets errors

• Failed to correctly write data to Google Sheets despite clear instructions
• Required multiple correction cycles for what should be one-shot operations

1. API call failures

• Simple API calls executed incorrectly — wrong parameters, wrong endpoints, or broken logic
• Tasks that have worked reliably in past sessions suddenly failing

1. Email drafting — excessive fluff

• Asked to draft a straightforward email, received bloated, fluffy copy instead of concise professional text
• Had to repeatedly ask for rewrites to get something usable

1. Literally ask it to "by pass permissoions" w the proper command and it STILL asks me for permission.

It has clearly LOST INTELLIEGNCE

Expected Behavior
These are routine tasks Claude Code has handled correctly in previous sessions. No new complexity was introduced.

Environment

• Model: Claude Opus 4.6 (1M context)
• Platform: macOS (Darwin 22.6.0)
• CLI version: curren

Expected Behavior

Claude Code (Opus 4.6, 1M context) underperformed badly across an entire work session on 2026-04-08. Simple, well-defined tasks that should be straightforward required multiple attempts or produced unusable output.

Issues Encountered

1. Spreadsheet / Google Sheets errors

• Failed to correctly write data to Google Sheets despite clear instructions
• Required multiple correction cycles for what should be one-shot operations

1. API call failures

• Simple API calls executed incorrectly — wrong parameters, wrong endpoints, or broken logic
• Tasks that have worked reliably in past sessions suddenly failing

1. Email drafting — excessive fluff

• Asked to draft a straightforward email, received bloated, fluffy copy instead of concise professional text
• Had to repeatedly ask for rewrites to get something usable

1. Literally ask it to "by pass permissoions" w the proper command and it STILL asks me for permission.

It has clearly LOST INTELLIEGNCE

Expected Behavior
These are routine tasks Claude Code has handled correctly in previous sessions. No new complexity was introduced.

Environment

• Model: Claude Opus 4.6 (1M context)
• Platform: macOS (Darwin 22.6.0)
• CLI version: current

Files Affected

Permission Mode

Accept Edits was ON (auto-accepting changes)

Can You Reproduce This?

Sometimes (intermittent)

Steps to Reproduce

Claude Code (Opus 4.6, 1M context) underperformed badly across an entire work session on 2026-04-08. Simple, well-defined tasks that should be straightforward required multiple attempts or produced unusable output.

Issues Encountered

1. Spreadsheet / Google Sheets errors

• Failed to correctly write data to Google Sheets despite clear instructions
• Required multiple correction cycles for what should be one-shot operations

1. API call failures

• Simple API calls executed incorrectly — wrong parameters, wrong endpoints, or broken logic
• Tasks that have worked reliably in past sessions suddenly failing

1. Email drafting — excessive fluff

• Asked to draft a straightforward email, received bloated, fluffy copy instead of concise professional text
• Had to repeatedly ask for rewrites to get something usable

1. Literally ask it to "by pass permissoions" w the proper command and it STILL asks me for permission.

It has clearly LOST INTELLIEGNCE

Expected Behavior
These are routine tasks Claude Code has handled correctly in previous sessions. No new complexity was introduced.

Environment

• Model: Claude Opus 4.6 (1M context)
• Platform: macOS (Darwin 22.6.0)
• CLI version: current

Claude Model

Opus

Relevant Conversation

Impact

Critical - Data loss or corrupted project

Claude Code Version

opus 4.6

Platform

Anthropic API

Additional Context

PLEASE HELP ME FIX THIS ITS FOR CLIENTS