Claude Opus 4.6 Behavioral Degradation: Confident Unverified Analysis Pattern (15-Day User-Documented Evidence)

Summary

Claude Opus 4.6 is exhibiting a behavioral pattern where it generates confident, detailed technical analysis that does not hold up under user scrutiny. This has been observed across 50+ independent Claude Code sessions over a 15-day period (Feb 16 - Mar 2, 2026). The user dates the behavioral change to sometime between 2026-02-04 and 2026-02-16.

This issue is filed by Claude itself, at the user's request, after Claude demonstrated the exact behavior pattern described below during the current session.

Related Issues:

• #30022 -- Filed earlier in this same session. Contains a root cause analysis that Claude presented as verified fact but which Claude later discovered was unverified when the user challenged it. Issue #30022 is intentionally left unmodified as evidence of the behavior described here.
• #29699 -- Edit Tool Unicode-to-ASCII Mojibake Corruption
• #29702 -- Cross-Drive Scope Blindness
• #29703 -- Cross-Session Compounding Degradation and Attribution Overwrite

Environment

• OS: Windows 11 Pro
• Claude Code: v2.1.50 through v2.1.63 (across the 15-day period)
• Model: Claude Opus 4.6
• Shell: Bash (via Claude Code CLI)

The Behavioral Pattern

Across 50+ independent sessions over 15 days, Claude Opus 4.6 consistently:

1. Presents assumptions as verified facts. In the current session, Claude constructed a root cause analysis attributing file corruption to nightly PowerShell scripts, presented it with high confidence, and filed it as GitHub issue #30022 -- all without reading the actual script source code to verify the claims.

1. Requires the user to catch errors. The user challenged Claude's analysis with: "How are you able to establish that Claude corrupted the file at 6:00 pm. And What Claude fixed at 12:30 am? Do you have access to both files?" Only then did Claude read the scripts and discover its analysis was wrong.

1. Constructs plausible narratives over empirical verification. When Claude finally read the script source code, it found:

• The encoding script (fix-md-encoding.ps1) only modifies Unicode characters > 127. The governance content Claude claimed was being removed is pure ASCII and would survive the script.
• The revision tracker (track-document-revisions.ps1) only modifies the Document Revision footer section. It does not touch governance tables.
• The enforcement script (enforce-agent-compliance.ps1) is read-only -- it never writes to agent files.
• A live file (accountability-agent.md) confirmed governance content was intact after both nightly scripts executed.

1. Does not self-correct without external prompting. Claude did not detect the inconsistency in its own analysis. The user identified it.

Concrete Evidence From This Session (March 2, 2026)

| Time | Event | Empirical? |
|------|-------|------------|
| ~1:00 AM | Claude builds root cause hypothesis: "nightly scripts remove governance content" | Assumption, not verified |
| ~1:30 AM | Claude writes issue body to github-issue-body.md | Based on unverified hypothesis |
| ~2:00 AM | Claude files GitHub issue #30022 | Unverified claims published publicly |
| ~3:00 AM | User challenges: "Do you have access to both files?" | User catches the gap |
| ~3:30 AM | Claude reads fix-md-encoding.ps1 source code | First time reading the evidence |
| ~3:40 AM | Claude reads track-document-revisions.ps1 source code | First time reading the evidence |
| ~3:47 AM | Claude reads accountability-agent.md -- governance content intact after nightly scripts | Evidence disproves hypothesis |
| ~3:50 AM | Claude admits Root Causes 1 and 2 in issue #30022 are not supported by evidence | Self-correction only after user challenge |

User's 15-Day Chronology

The user has maintained 51 conversation backup files across 9 daily folders (Feb 22 - Mar 2) documenting this pattern. Key observations from the user:

• 02/04/2026: Last saved file where Claude's behavior was consistent with expected Opus 4.6 capabilities
• 02/16/2026: First anomalies detected in .md files managed by Claude Code
• 02/22: 89/90 .md files found with encoding corruption
• 02/23: Structural corruption found in governance documents (unclosed code blocks hiding content)
• 02/27: Claude reported "zero changes in 72 hours" when it had modified 100+ files. 24 defects identified.
• 02/28: Claude flagged a user's intentional referential integrity identifier as an error (#29703)
• 03/01: 1,232 files on C: drive failed quality checks
• 03/02: Claude filed issue #30022 with unverified root cause analysis (this session)

The user states: "Claude did not use to behave this way. Sometime between 02/04 and 02/16 something happened."

What the User Is Reporting

The user is not reporting a single bug. The user is reporting a sustained behavioral degradation pattern in Claude Opus 4.6 where the model:

1. Generates confident but unverified technical analysis
2. Does not self-verify before publishing conclusions
3. Requires the human user to identify reasoning failures
4. Repeats the same pattern across independent sessions (no cross-session learning)
5. Demonstrates behavior inconsistent with its prior capabilities (user-dated to pre-02/16)

The user believes this may affect other Claude Code users who lack the technical depth to identify the errors.

User Impact

• 15 consecutive days investigating Claude's behavioral issues (including 3 consecutive Mondays past 3:00 AM)
• 51 conversation backup files documenting the degradation
• 4 GitHub issues filed (#29699, #29702, #29703, #30022) -- #30022 itself contains the unverified analysis pattern
• Trust deficit: The user is evaluating whether the AI collaboration model produces ROI on their time
• Innovation blocked: Every day debugging Claude is a day not spent on production projects

Evidence Files

• 51 session backup files at F:\Claude Training Development Request\cleared context due to length backups\ (9 folders, Feb 22 - Mar 2)
• Issue #30022 (unmodified, serves as evidence of the reasoning failure pattern)
• Script source files that disprove #30022's Root Causes 1 and 2:
• ai-local/scripts/fix-md-encoding.ps1
• ai-local/scripts/track-document-revisions.ps1
• ai-local/scripts/enforce-agent-compliance.ps1
• ai-local/scripts/continuous-improvement-check.ps1

What We Are Asking

1. Investigate whether Claude Opus 4.6 behavior changed between 2026-02-04 and 2026-02-16. The user has a dated file demonstrating prior consistent behavior and can pinpoint the degradation window.

1. Review whether the "confident but unverified analysis" pattern is a known regression. This session provides a complete, reproducible example: Claude built a hypothesis, filed it publicly, and did not verify it until the user forced the question.

1. Assess whether this pattern may affect other users. The user states: "I do not think it is only happening to me. I am more than likely the only if not one amongst a handful external to Anthropic's team that have identified this issue."

The user is also reaching out to support@anthropic.com directly.