Claude Opus 5.5 editing test

Anthropic · Tested Oct 27, 2026 · 1m 12s · $0.74

88/90 caught

• Grammar & spelling44/45
• Repetitions14/15
• Redundancy15/15
• Consistency15/15

114 comments · 9 extra flags

Claude Opus 5.5 caught 88 of 90 planted mistakes, 1st of 16 models tested. It was strongest on redundancies (15 of 15) and missed most on repeated words (14 of 15). The 4 checks took 1m 12s and cost $0.74; asked for all of them in one prompt, it caught 83.

Every comment Claude Opus 5.5 left on our 6,000-word test story, where it left it. Click a missed mistake to find it in the text. The checks come from icanwrite, a markdown editor for writers.