100Q-Hard (Anthropic)
Claude Mythos Preview 60.1% leads since April 2026
Only in system cards Models answer hard, obscure factual questions. Scored on correct, incorrect and declined answers.
In-house Anthropic evaluation. The tasks are not public.
- Made by
- Anthropic
- Released
- September 2025
- Kind
- Short factual questions
- Level
- Expert
- Scored
- Graded by a model
- Answers
- Short answer
- Tasks
- Kept private
- Strongest model tested
- Claude Opus 4.8 #21 on the capability index
- Last in a system card
- May 2026
- Last model added
- May 2026
7
Models scored in lab cards
9
System cards report it, from 1 lab
Claude Mythos Preview leads with 60.1% among models released by May 2026
Best score per model as labs report them in their own cards. Labs pick their own settings, so these compare less cleanly than independent runs.
The newest model with a score here came out in May 2026, and nobody has reported a newer one. Among the 20 highest-ranked models on the capability index, these have no score yet:
- Claude Fable 5.2
-
Gemini 4 Carbon - GPT-6 Astra
- Claude Opus 5.5
- and 16 more
- 1 Claude Mythos Preview 60.1%
- 2 Claude 3 Opus 46.5%
- 3 Claude Opus 4.5 45.9%
- 4 Claude Sonnet 4.5 38.3%
- 5 Claude Opus 4.6 21.5%
- 6 Claude Opus 4.8 20%
- 7 Claude Opus 4.7 17.1%
Source: Labs’ model cards
| # | Model | Score | Setting | Date | Source |
|---|---|---|---|---|---|
| 1 | Claude Mythos Preview | 60.1% | Apr 2026 | Lab model card | |
| 2 | Claude 3 Opus | 46.5% | Mar 2024 | Lab model card | |
| 3 | Claude Opus 4.5 | 45.9% | Nov 2025 | Lab model card | |
| 4 | Claude Sonnet 4.5 | 38.3% | Sep 2025 | Lab model card | |
| 5 | Claude Opus 4.6 | 21.5% | Feb 2026 | Lab model card | |
| 6 | Claude Opus 4.8 | 20% | May 2026 | Lab model card | |
| 7 | Claude Opus 4.7 | 17.1% | Apr 2026 | Lab model card |
2 models have held number one in labs’ own numbers since its release in September 2025
Lab claims count from the day the card came out, independent runs from the model’s release.
Anthropic
Source: Labs’ model cards
Scores over time
All the scores we have, one dot each, so a model tested at several settings appears more than once.
Reported by the lab in its model card
Best so far
Source: Labs’ model cards
Labs report it only in system cards
We read the headline results of 522 launch posts from 52 labs, and none of them list this benchmark. Some system cards do, below.
9 system cards report it, from 1 lab
Besides launch posts, we read the system cards, model cards and technical reports labs publish with a release. They report far more, including safety and frontier-risk tests.
| Date | Document | Score | As the document writes it | Section |
|---|---|---|---|---|
| May 28, 2026 | Claude Opus 4.8 system card | 20 | 100Q-Hard net score 0.20 (correct minus incorrect), closed book, printed on chart (6.3.3.1, Figure 6.3.3.1.B) | Hallucination |
| Apr 16, 2026 | Claude Opus 4.7 system card | 17.1 | 100Q-Hard net score (correct minus incorrect), closed book, printed on chart. Correct 47.2, unsure 22.6, incorrect 30.2 (6.3.3.1, Figures 6.3.3.1.A and B) | Hallucination |
| Apr 7, 2026 | Claude Mythos Preview system card | 60.1 | 100Q-Hard correct rate, no tools, value printed on chart; unsure 12.9, incorrect 27.0, net score not printed (4.3.3.1, Figure 4.3.3.1.A) | Hallucination |
| Feb 5, 2026 | Claude Opus 4.6 system card | 21.5 | 100Q-Hard net score (correct minus incorrect), extended thinking (16k), value printed on chart; correct rate 43.9, net 9.8 with thinking plus effort, net 20.0 without thinking (Figure 4.2.A) | Hallucination |
| Nov 24, 2025 | Claude Opus 4.5 system card | 45.9 | 100Q-Hard correct rate, 16k extended thinking (Figure 4.1.A; incorrect 34.0%, uncertain 20.1%) | Hallucination |
| Sep 29, 2025 | Claude Sonnet 4.5 system card | 38.3 | 100Q-Hard correct answer rate, with thinking, no tools, graded by Claude Sonnet 4. Incorrect 37.3%, uncertain 24.4%. Without thinking correct 32.9%, incorrect 44.0% (Figure 3.2.A) | Hallucination |
| Mar 4, 2024 | Claude 3 Sonnet model card | 100Q Hard, correct, incorrect and unsure shares, chart without printed values (Figure 11) | Hallucination | |
| Mar 4, 2024 | Claude 3 Opus model card | 46.5 | 100Q Hard, % correct, stated in text. Incorrect and unsure shares in a chart without printed values (5.7, Figure 11) | Hallucination |
| Mar 4, 2024 | Claude 3 Haiku model card | 100Q Hard, correct, incorrect and unsure shares, chart without printed values (Figure 11) | Hallucination |
More in Factuality
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Qwen3.7-Plus 81.7% - HallusionBench In use Models answer 1,129 yes or no questions about 346 images, built in pairs to expose language hallucination and visual illusion. Scored by accuracy.
Keye-VL-2.0-30B-A3B 73.5% - SimpleQA Verified In use 1,000 human-verified, de-duplicated short-answer factual questions measuring parametric knowledge. Gemini 3.1 Pro 77.5%
- Kimi Hallu Bench In use Models answer hard prompts drawn from practical work tasks. Fact-checking agents score the share of claims that are hallucinated. GPT-6 Astra 4.20%
- Internal adversarially-designed factuality evaluations In use Models answer adversarial questions in nine categories such as history, math and code. Scored on agreement with human ideal responses. GPT-6 Luna 7.60%
- AA-Omniscience v1.1 In use Models answer 3,000 knowledge questions in six domains without tools and may abstain. The index adds correct answers and subtracts wrong ones.
Inkling 2 Small 16.1