← All models Claude Opus 4.8 editing test Anthropic · Tested Oct 28, 2026 · 55s · $0.66
Four checks All in one 65/90 caught
Grammar & spelling 42/45 Repetitions 3/15 Redundancy 11/15 Consistency 9/15 226 comments · 6 extra flags
Claude Opus 4.8 caught 65 of 90 planted mistakes, 13th of 16 models tested. It was strongest on grammar and spelling (42 of 45) and missed most on repeated words (3 of 15). The 4 checks took 55s and cost $0.66; asked for all of them in one prompt, it caught 65.
Every comment Claude Opus 4.8 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.
Missed · 25
any other shop: the bakery is on Wharf Street “longer than any shop on Wharf Street” Fragment: the survey has no verb “The survey from twelve years ago, which an engineer from the county” 'one of those who' takes a plural verb: were “one of the last binders in New England who was still” Close: tired … tired “thin, tired ring” Close: careful … careful “his careful hands” Distinctive, chapters apart: pewter “Pewter light from the tall back window” Distinctive, chapters apart: threadbare “a threadbare, flour-dusted sweater” Close: silence … silent “The silence in the workshop” Distinctive, chapters apart: meticulous “His records were meticulous” Close: neatly … neat “neatly labeled” Distinctive, chapters apart: gleaming “a gleaming pair of shoes” Distinctive, chapters apart: sodden “carrying sodden leaves” Distinctive, chapters apart: brittle “a short, brittle sound” Distinctive, chapters apart: stubbornly “which stuck stubbornly” Close: remembered … memory “her hands remembered” twins are two “the two twins” an agreement is mutual “By mutual agreement” a haven is safe “a safe haven” began is first “the week we first began” The bakery has three tables; she sits at the fourth “three small tables” Said on Friday: the day after tomorrow is Sunday “On Friday a woman knocked” Tea becomes coffee “poured her a mug of tea” Tomas beside him: two decades, then thirty years “for most of two decades” The bakery: two doors down, then a ten-minute walk “BAKERY TWO DOORS DOWN” Writes left-handed, then with his right “He had been left-handed”