Claude Opus 5.5 simply writes better.
Em dashes fall from 15.2 to 0.8 per 1,000 words, a 95% drop, while semicolons fall 73%.
But Opus 5.5 did not become terse. It actually became 6% longer, from 453 to 481 words per answer, while average sentence length fell 17%, from 12.14 to 10.03 words.
We analyzed how @claudeai’s Opus 5.5 writes compared with Opus 5 across high-reasoning Text Arena outputs. 10 of 12 writing measures moved in a better direction...