On September 29, IT Home reported a September 26 post by @arena that compared Claude Opus 5.5 with Opus 5 on writing metrics. Arena looked at high-reasoning replies on Text Arena in August and September 2026. Ten of twelve metrics moved in the direction Arena treats as an improvement. This piece did not open the post or the chart, and it does not treat “improvement” as a measured gain in reading quality.

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Iron-gall ink: a long stroke breaks and leaves a single dot.
A long stroke stops and becomes a dot. That is fewer dashes, not a scan of a manuscript. An illustration, not a news photo., AI-generated illustration, not a news photograph

The largest change is the dash. Opus 5 used 15.2 dashes per 1,000 words. Opus 5.5 used 0.8, about 95% fewer. Semicolons fell from 6.10 per 1,000 words to 1.64, a 73% drop. IT Home reads that as fewer punctuation habits that are easy to recognize.

Sentences also got shorter. Opus 5.5 averages 10.03 words. Opus 5 averages 12.14. The answers themselves did not get shorter. Opus 5 averages 453 words. Opus 5.5 averages 481, described as the longest average Opus answer in the comparison. Shorter sentences and longer answers are both in the same set of counts.

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要点

  • The sample is high-reasoning Text Arena replies from August and September 2026. The post is dated September 26.
  • Dashes fell from 15.2 per 1,000 words to 0.8, about 95% fewer. Semicolons fell from 6.10 to 1.64, down 73%.
  • Average sentence length fell from 12.14 words to 10.03. Average answers grew from 453 words to 481.
  • Ten of twelve “improvements” are Arena’s label. The original post was not opened.