Claude Opus 5.5 uses 95% fewer em dashes, but its answers are getting longer

Summary

Anthropic's Claude Opus 5.5 writes differently from Opus 5, according to an analysis by the benchmarking tool Arena. Arena found fewer obvious AI writing patterns and shorter sentences, with em dashes falling from 15.2 to 0.8 per 1,000 words. The trade-off is that average answers grew from 453 to 481 words, making Opus 5.5 the longest-writing Opus model in the comparison.

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