Chat model

Claude Opus 5.5

high reasoning · 16 questions per request

95.0% of the 2,198 questions right (94.0% to 95.8%, 95% interval). Back to the leaderboard.

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: 278, 28 October 2026

Settings

Reasoning: high
Request format: 16 questions per request
Requests at once: 1
Temperature: not recorded
Harness seed: 0
Harness commit: 0fbd97b0899d
Prompt version: 254597b8be16

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

Results

Questions	Accuracy	95% interval	Right
All questions	95.0%	94.0% to 95.8%	2,088 of 2,198
Reading	95.6%	93.7% to 96.9%	627 of 656
Grammar	94.7%	93.5% to 95.8%	1,461 of 1,542

Comparison group: ef. Compare with another setup.

Accuracy by topic

Topic	Part	Accuracy	Right
Word and phrase meanings	Reading	96.2%	126 of 131
Sentence meanings	Reading	98.1%	151 of 154
How a writer explains and develops ideas	Reading	90.0%	63 of 70
Topic and main point of a paragraph	Reading	99.0%	97 of 98
How a paragraph fits together	Reading	90.6%	96 of 106
Details that support a paragraph’s main point	Reading	96.9%	94 of 97
Word types, such as nouns and verbs	Grammar	97.1%	136 of 140
Groups of words built around a noun	Grammar	98.5%	64 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	98.7%	78 of 79
How words are built	Grammar	94.2%	65 of 69
The roles of words and phrases in a sentence	Grammar	97.2%	141 of 145
How verbs show who acts and who receives the action	Grammar	95.9%	71 of 74
Types of sentences	Grammar	95.3%	81 of 85
Questions combining several grammar topics	Grammar	94.1%	207 of 220
Sound patterns and changes	Grammar	90.9%	70 of 77
Spelling	Grammar	90.2%	120 of 133
Punctuation	Grammar	88.9%	104 of 117
Problems in sentence wording	Grammar	93.7%	164 of 175

Confidence

Answers kept at 99% or more: 0, of which 0 wrong; 2,198 skipped, the model less than 99% sure
Calibration gap: 14.6 points
AUROC, all questions: 0.84 0.79 to 0.88
AUROC, reading: 0.92 0.86 to 0.96
AUROC, grammar: 0.81 0.75 to 0.86
Brier score: 0.066
Accuracy of its surest answers: most confident fifth: 99.4% right; most confident half: 98.9% right; most confident four fifths: 98.2% right
Typical score of a right answer: 85.0%
Typical score of a wrong answer: 60.0%

Repeats

Run 5 times on a sample of 200 questions.

Answers changed in 5 runs: 5 of 200
Same wrong answer in all 5: 3 of 200
Wrong in at least one run: 8 of 200
Accuracy in each run: 98.5%, 97.5%, 97.5%, 97.0%, 98.0%

Latency

Latency, median request: 22.1 s (this run)
Latency, 90th percentile: 45.0 s
Requests at once: 1
Throughput: 39.0 questions per minute of request time
Request time: 56.3 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: $6.51
Whole run: $14.31
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: 568
Output tokens per question: 155