Claude Opus 5.5 Cuts Dash Usage by About 95% in Writing Test

Arena posted on X that a writing metrics test found clear punctuation changes in Anthropic's Claude Opus 5.5 compared with Opus 5.

The data shows Opus 5.5 used 0.8 dashes per 1,000 words, down from 15.2 for Opus 5, a drop of about 95%. Semicolon use also fell from 6.10 to 1.64, a 73% decrease.

Opus 5.5's average sentence length was 10.03 words, lower than Opus 5's 12.14 words, making its wording more concise overall. However, its average answer length rose from 453 words to 481 words.

Arena analyzed high-reasoning Text Arena responses from August and September 2026. Of 12 writing metrics, 10 moved in what Arena considers an improved direction.