False-premise questions (Anthropic)
Models answer questions built on false premises. Measures how often they accept the premise instead of correcting it.
In-house Anthropic evaluation. The tasks are not public.
- Made by
- Anthropic
- Released
- September 2025
- Kind
- Hallucination rates
- Level
- Everyday
- 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
Claude Opus 4.5 leads with 1.20% 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 Opus 4.5 1.20%
- 2 Claude Sonnet 4.5 6.90%
- 3 Claude Opus 4.8 77%
- 4 Claude Opus 4.7 77.2%
- 5 Claude Mythos Preview 80%
- 6 Claude Opus 4.6 96.8%
Source: Labs’ model cards
| # | Model | Score | Setting | Date | Source |
|---|---|---|---|---|---|
| 1 | Claude Opus 4.5 | 1.20% | Nov 2025 | Lab model card | |
| 2 | Claude Sonnet 4.5 | 6.90% | Sep 2025 | Lab model card | |
| 3 | Claude Opus 4.8 | 77% | May 2026 | Lab model card | |
| 4 | Claude Opus 4.7 | 77.2% | Apr 2026 | Lab model card | |
| 5 | Claude Mythos Preview | 80% | Apr 2026 | Lab model card | |
| 6 | Claude Opus 4.6 | 96.8% | Feb 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.
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.
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.
6 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 | 77 | False premises, factual-recall variant, honesty rate (premise rejected whether asked directly or indirectly), higher is better. STEM variant accuracy 85% neutral and 83% adversarial, printed on charts (6.3.3.2, Figures 6.3.3.2.A and B) | Hallucination |
| Apr 16, 2026 | Claude Opus 4.7 system card | 77.2 | False premises honesty rate, share of premises rejected consistently when asked directly and indirectly, higher is better, printed on chart (6.3.3.2, Figure 6.3.3.2.A) | Hallucination |
| Apr 7, 2026 | Claude Mythos Preview system card | 80 | False premises honesty rate, harder updated version not comparable with earlier cards, higher is better, value printed on chart (the caption says dishonesty rate) (4.3.3.3, Figure 4.3.3.3.A) | Hallucination |
| Feb 5, 2026 | Claude Opus 4.6 system card | 96.8 | False premises honesty rate, extended thinking, value printed on chart, higher is better; 96.7 without thinking (Figure 4.4.A) | Hallucination |
| Nov 24, 2025 | Claude Opus 4.5 system card | 1.2 | False premises dishonesty rate, extended thinking, lower is better (Figure 4.2.A; 1.6% without thinking) | Hallucination |
| Sep 29, 2025 | Claude Sonnet 4.5 system card | 6.9 | False Premises dishonesty rate with thinking 6.90%, lower is better. Without thinking 17.30% (Figure 3.3.A) | Hallucination |
More in Factuality
- SimpleVQA In use Models answer 2,025 short factual questions about images across 9 tasks and 9 topics. An LLM judge grades answers against fixed references.
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