Text Arena: Opus 5.5 Writes More Like Humans, Em Dash Use Down 95%

Text Arena compared Claude Opus 5.5 against Opus 5 on high-reasoning writing outputs and found that 10 of 12 writing metrics moved in a better direction, with the overall style becoming more human-like. Reddit user Outside-Iron-8242 was the first to surface the ArenaAI comparison, noting that Opus 5.5 almost entirely stopped using em dashes unlike its predecessor; the finding was then amplified by rohanpaulai and MaziyarPanahi.

Confirmed

• Em dash usage per thousand words dropped by roughly 95%; em dashes have long been considered a telltale AI writing artifact
• Average sentence length shrank by 17%
• Long-word ratio fell from 41.7% to 38.6%, the lowest of any Claude model analyzed
• 10 of 12 writing metrics improved

Why it matters

• The sharp decline in em dashes, alongside shorter sentences and fewer long words, suggests Anthropic deliberately or incidentally reduced AI-flavored writing in Opus 5.5
• This is a textbook case of observable model style drift, giving users quantitative evidence for assessing new-model readability

2026-09-26 ~ 2026-09-27 · 5 related posts

• [source] Opus 5.5 writes shorter sentences and 95% fewer em dashes, but hedges rise 97% — arena · 2026-09-26
• Opus 5.5 cuts em dashes 95% and shortens sentences 17%, Text Arena writing analysis finds — devdigest · 2026-09-26
• [source] Opus 5.5 almost entirely stopped using em dashes, users observe — Outside-Iron-8242 · 2026-09-26
• Claude Opus 5.5 Writing Analysis: 10 of 12 Metrics Improve, Sentences 17% Shorter — MaziyarPanahi · 2026-09-27

1 near-duplicate retellings: rohanpaul_ai