Degradation Claude Code: reasoning depth -73%

Claude Code Degradation: 73% Drop in Reasoning Depth, Costs Surge 122x

AMD's AI division director Stella Lourenco analyzed 6,852 Claude Code sessions, uncovering a 73% plunge in reasoning depth between January and March 2026. On identical tasks and prompts, the Read:Edit ratio dropped from 6.6 to 2.0, while API costs skyrocketed 122 times—from $345 to $42,121 for the same workload. Now, one in three edits targets files the model never even opened.

Lourenco shared raw data from 234,760 tool calls and 17,871 reasoning blocks in GitHub issue #42796, declaring: "Claude cannot be trusted to perform complex engineering tasks." The issue drew 368 comments before being closed on April 13.

Lexical Indicators of Degradation

Frequency analysis of prompts revealed a shift in emotional tone:

• "simplest" surged 642% (from 0.01 to 0.09 per thousand calls);
• "stop" +87%;
• "fuck" +68%;
• "great" −47%;
• "please" −49%;
• "commit" −58%.

The positive-to-negative ratio worsened from 4.4:1 to 3.0:1, mirroring real developer frustration in production scenarios with systems programming.

Three Confirmed Behavior Changes

Anthropic rolled out three unannounced updates, verified by docs and Claude Code dev Boris Cherni's responses:

• February 9: Adaptive Thinking. Switched from fixed budget_tokens to self-assessed reasoning volume. Complex steps got 0 reasoning tokens, sparking hallucinations (fake SHAs, nonexistent packages).

• March 3: effort high → medium. Dropped default effort level without notice. Hits hard in long autonomous sessions (30+ minutes).

• March 5–12: thinking redaction. Visibility of reasoning blocks fell from 100% (Jan 30) to 0% (Mar 12). Cherni called it a UI tweak, but data shows a prior 67% reasoning dip.

Read:Edit Metric and Blind Edits

The key gauge: ratio of files read to files edited:

| Period | Read:Edit | Blind Edits (%) | Full-File Write (%) |

|---------|-----------|-----------------|---------------------|

| January | 6.6 | 6.2 | 4.9 |

| March | 2.0 | 33.7 | 11.1 |

The model skips dependencies, headers, and tests before editing, breaking builds in compiler and GPU driver projects. Reasoning loops tripled; subagents made up 26% of requests.

API calls ballooned 80x (1,498 → 119,341), output tokens 64x.

Workarounds to Restore Performance

Anthropic's temporary fixes:

export CLAUDE_CODE_DISABLE_ADAPTIVE_THINKING=1
export CLAUDE_CODE_EFFORT_LEVEL=max

Or in-session: /effort max.

For ~/.claude/settings.json:

{
  "env": {
    "CLAUDE_CODE_DISABLE_ADAPTIVE_THINKING": "1",
    "CLAUDE_CODE_EFFORT_LEVEL": "max"
  }
}

Marginlab's SWE-Bench-Pro data shows workarounds recover to 56% performance (from 50%). Tips: break up sessions, use /clear, run off-peak (reasoning 28% higher at 11 PM PST).

How to Reproduce the Degradation

Test on your tasks:

• Pick a multi-file task (refactor, bugfix).
• Check status: /effort, echo $CLAUDE_CODE_DISABLE_ADAPTIVE_THINKING.
• Run with defaults, log Read:Edit.
• Apply workaround and rerun.
• Compare metrics.

The gap confirms it's hitting your workflow.

Key Takeaways

• Reasoning depth tanked 73% due to Adaptive Thinking and lower effort;
• Read:Edit crashed from 6.6 to 2.0, blind edits hit 33.7%;
• API costs ×122 for the same tasks;
• Workarounds deliver: two env vars restore ~90% performance;
• Track Read:Edit as your degradation canary.

Analysis Limitations

Data from one user (AMD, MLIR/GPU, 50 agents). Thinking-signature correlation 0.971 (Pearson r), but extrapolating to web dev is risky. Backing evidence: SWE-Bench-Pro (56%→50%), 368 comments, 30 r/ClaudeAI threads. No changelog for model behavior is an industry-wide issue.

— Editorial Team