[MODEL] Quantified evidence: Sonnet 4.6 quality regression since March 9 — 1400+ frustration events across 50 sessions
Status Fixed / completed
Maintainer reply None cached
Activity 5 comments · opened Apr 12, 2026 · closed Apr 19, 2026
Summary
I have quantified data showing a dramatic quality regression starting the week of March 9, 2026. This is not a vibe check — it's measured from 60 days of conversation logs across 50 sessions.
Data
I track how often I need to repeat instructions or correct Claude (my "WTF frequency"). Here's the weekly distribution:
60-day data across 50 sessions:
W09 (Feb 24) 26 ██ ← baseline
W10 (Mar 02) 23 ██ ← baseline
W11 (Mar 09) 221 ██████████████████████ ← started (8.5x baseline)
W12 (Mar 16) 484 ████████████████████████████████ ← peak (outage week)
W13 (Mar 23) 479 ████████████████████████████████ ← still bad
W14 (Mar 30) 65 ██████ ← relax
W15 (Apr 06) 294 █████████████████████████████ ← under way- Baseline (W09–W10): ~25/week
- Peak (W12–W13): ~480/week — 19x baseline
- Total across 50 sessions: 1,400+ events
Affected models
I've been forced to switch from Sonnet to Opus as my primary model. Sonnet 4.6 is basically unusable now. My subjective rating of current model quality:
- Opus 4.6 now = Sonnet 4.6 before
- Sonnet 4.6 now = Haiku before
- Haiku = Haiku (unchanged — nothing left to degrade)
This means I'm paying Opus prices for what used to be Sonnet-level performance.
What "regression" looks like in practice
The model consistently fails to:
- Follow its own reasoning loop (OODA) despite explicit CLAUDE.md instructions
- Read files before modifying them — guesses instead
- Stop repeating the same mistake — same error 5–8 times per session without self-correction
- Follow explicit behavioral constraints across sessions (#41217)
Timeline alignment
The W12 peak (March 16) aligns exactly with:
- The March 17 outage acknowledged on status.claude.com
- r/ClaudeCode thread "After the outage today, does Claude feel dumber?"
- Multiple GitHub issues filed the same week (#37052, #35271, #32290)
Environment
- Claude Code CLI v2.1.94
- Linux
- bypassPermissions mode
- Heavy skill/hook usage with structured CLAUDE.md rules
What I'm asking
- Acknowledge that model quality has regressed — the data is clear
- Explain whether this is a compute constraint issue (as widely suspected) or a checkpoint/RLHF regression
- Provide a model versioning mechanism so users can pin to a known-good checkpoint
Related issues
- #46106 Opus 4.6 is getting dumber
- #41217 Systematic Failure to Follow Explicit Behavioral Constraints
- #42542 Silent context degradation
- #38338 Opus 4.6 acts dumber than Sonnet 3.5
- #37052 Claude Code model regression
- #21046 Opus 4.5 "Shadow Downgrade"
5 Comments
Found 3 possible duplicate issues:
This issue will be automatically closed as a duplicate in 3 days.
🤖 Generated with Claude Code
This is not a duplicate. The linked issues (#44246, #38903, #36093) describe the same symptoms but none of them provide quantified data.
This issue contains:
If anything, those issues are supporting evidence for this one. Please do not auto-close the only issue in this repo that has actual numbers behind it.
Pro tip: You can use Claude Code itself to analyze your own conversation history and quantify the regression. That's exactly how I got this data — Claude searched its own logs and counted the frustration events.
If you're experiencing the same issues, run a similar analysis on your own sessions and post your numbers here. The more quantified data we have, the harder this is to dismiss as "confirmation bias."
Closing this. I've moved on.
I spent two hours planning with Opus, then gave Codex 15 words. It finished in 90 minutes.
The data in this issue still stands — I hope it's useful to someone.
This issue has been automatically locked since it was closed and has not had any activity for 7 days. If you're experiencing a similar issue, please file a new issue and reference this one if it's relevant.