Chat model

Claude Opus 5.5

low reasoning · 1 question per request

93.3% of the 2,198 questions right (92.2% to 94.3%, 95% interval). Back to the leaderboard.

We also ran this setup at 16 questions per request: Claude Opus 5.5 · low reasoning · 16 questions per request.

Which decision model can go first in front of it? See the Routing tab.

How we called it

Kind: Chat model
Access: Claude Code CLI, Claude subscription
Paid as: Subscription
Model ID: claude-opus-5-5
Confidence from: Written estimate
Run: 192, 13 October 2026

Settings

Reasoning: low
Request format: 1 question per request
Requests at once: 1
Temperature: not recorded
Harness seed: 0
Harness commit: 54043fd92cd5
Prompt version: 254597b8be16

Effort levels (Anthropic's effort documentation, read 28 October 2026): low, medium (default), high, xhigh, max. Top level: max. This run: low.

Results

Questions	Accuracy	95% interval	Right
All questions	93.3%	92.2% to 94.3%	2,051 of 2,198
Reading	95.7%	93.9% to 97.0%	628 of 656
Grammar	92.3%	90.8% to 93.5%	1,423 of 1,542

Comparison group: fgh. Compare with another setup.

Accuracy by topic

Topic	Part	Accuracy	Right
Word and phrase meanings	Reading	97.7%	128 of 131
Sentence meanings	Reading	96.8%	149 of 154
How a writer explains and develops ideas	Reading	85.7%	60 of 70
Topic and main point of a paragraph	Reading	96.9%	95 of 98
How a paragraph fits together	Reading	94.3%	100 of 106
Details that support a paragraph’s main point	Reading	99.0%	96 of 97
Word types, such as nouns and verbs	Grammar	95.7%	134 of 140
Groups of words built around a noun	Grammar	96.9%	63 of 65
Verbs and their forms	Grammar	97.8%	89 of 91
Verb forms used like nouns or modifiers	Grammar	98.6%	71 of 72
Word endings and what they do	Grammar	97.5%	77 of 79
How words are built	Grammar	92.8%	64 of 69
The roles of words and phrases in a sentence	Grammar	95.9%	139 of 145
How verbs show who acts and who receives the action	Grammar	94.6%	70 of 74
Types of sentences	Grammar	91.8%	78 of 85
Questions combining several grammar topics	Grammar	90.5%	199 of 220
Sound patterns and changes	Grammar	85.7%	66 of 77
Spelling	Grammar	85.0%	113 of 133
Punctuation	Grammar	82.1%	96 of 117
Problems in sentence wording	Grammar	93.7%	164 of 175

Confidence

Answers kept at 99% or more: 1, of which 0 wrong (share right: 20.7% to 100.0%, 95% interval); 2,197 skipped, the model less than 99% sure
Calibration gap: 10.2 points
AUROC, all questions: 0.88 0.86 to 0.91
AUROC, reading: 0.95 0.93 to 0.97
AUROC, grammar: 0.86 0.82 to 0.89
Brier score: 0.060
Accuracy of its surest answers: most confident fifth: 99.9% right; most confident half: 99.3% right; most confident four fifths: 97.9% right
Typical score of a right answer: 88.0%
Typical score of a wrong answer: 60.0%

Repeats

We did not repeat this setup.

Latency

Latency, median request: 3.71 s (this run)
Latency, 90th percentile: 5.88 s
Requests at once: 1
Throughput: 14.5 questions per minute of request time
Request time: 151.4 minutes, over the requests whose answers were kept

Latency: the time from sending one request to receiving its answer, measured from our computer, network and any retries within the request included. Request time: the time at least one request was in flight, over the requests whose answers were kept. It is not the run's elapsed time: it leaves out requests that failed and any pause before a run was resumed.

Cost

$ per 1,000 questions: $11.61
Whole run: $25.52
Basis: Subscription run priced as if we had used the API
Price: $4 input, $0.20 cached input, $5 5-minute cache writes, $8 1-hour cache writes, $20 output per 1M tokens (source, 2026-10-08)
Input tokens per question: 1,584
Output tokens per question: 196