Thought Leadership
An evaluation by Arena shows: Claude Opus 5.5 writes shorter sentences and almost dispenses with em dashes. However, the responses are getting longer.
Anthropic’s AI model Claude Opus 5.5 writes differently than its predecessor Opus 5. This is according to an evaluation by the benchmark platform Arena. It analyzed responses from the Text Arena involving high reasoning effort from the months of August and September 2026. For 10 out of 12 analyzed writing characteristics, Arena noted changes in a direction that the platform classifies as an improvement.
Claude Opus 5.5: Em Dashes Almost Disappeared
The evaluation shows the most distinct difference in em dashes, the long dash that is often considered a typical characteristic of AI-generated text. Opus 5 used 15.2 em dashes per 1,000 words, while Opus 5.5 used only 0.8. That corresponds to a decrease of around 95 percent. The new model also uses semicolons less frequently: Their number dropped from 6.10 to 1.64 per 1,000 words.
Shorter Sentences, Simpler Word Choice
The sentences of Opus 5.5 are on average 10.03 words long, compared to 12.14 words for Opus 5. Additionally, Arena noted fewer long sentences and simpler word choices. Patterns considered typical for AI text appear less frequently according to the analysis.
Responses Are Getting Longer
At the same time, responses have become more extensive overall. The average length rose from 453 to 481 words. Opus 5.5 is thus the Opus model with the longest responses in comparison.
(Editorial Team)
