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Opus 5.5 code gets messier but doesn't fail, user finds

A user tested Anthropic's Opus 5.5 model on the SlopCodeBench benchmark, which evaluates an AI's ability to add new features to its own code without introducing errors. The tests revealed that Opus 5.5's code did become messier over time, with increased structural erosion and verbosity in many problems. However, this code messiness did not correlate with a decrease in its ability to pass checkpoints or a higher rate of regression in previously passing tests. Interestingly, while code size impacted cost, code messiness itself did not predict higher costs for subsequent checkpoints. AI

IMPACT Suggests that code messiness may not be a direct predictor of AI model failure in coding tasks, potentially impacting how code quality metrics are used.

RANK_REASON User-conducted research/benchmark of an existing model. [lever_c_demoted from research: ic=1 ai=1.0]

Read on r/ClaudeAI →

AI-generated summary · Google Gemini · from 1 sources. How we write summaries →

Opus 5.5 code gets messier but doesn't fail, user finds

How we ranked this

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14 / 100
Composite score across the factors below. Higher = stronger signal that this story matters right now.
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Tool
User-conducted research/benchmark of an existing model. [lever_c_demoted from research: ic=1 ai=1.0]
Source corroboration
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Only one publisher covered this so far. Single-source stories can still rank when the publisher is high-authority, but they lack cross-source corroboration.
Topics
model release, product
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High
Clearly on-topic for AI-industry coverage.
Story freshness
Breaking (< 6h)
Fresh story with cross-source coverage still developing. Ranking may shift as more sources report.

Full methodology in our editorial standards.

COVERAGE [1]

  1. r/ClaudeAI TIER_2 English(EN) · /u/aj_marshall ·

    Opus 5.5 writes slop code, but succeeds anyways. A research project inspired by SlopCodeBench

    <!-- SC_OFF --><div class="md"><p>A few months ago, I ran across this paper proposing a benchmark called SlopCodeBench. The idea is that you give an agent a problem split into a bunch of checkpoints, and at each one it has to add a new feature on top of its own old code without b…