# Can AI detectors catch Claude Haiku 5.5?

Source: https://toolbenchmarks.com/can-ai-detectors-catch/claude-haiku-5-5/  
Tested: 30 October 2026. Publisher: Tool Benchmarks. Data licence: CC BY 4.0.

> Usually. Claude Haiku 5.5 was the easiest of the four Claude models to detect. A majority of the seven free detectors we tested flagged 77.0% of its texts, Fast-DetectGPT caught 88.9% and Desklib 74.6%. Even so, roughly one Haiku text in nine slipped past the best detector.

| Detector | Share flagged as AI |
|---|---|
| Fast-DetectGPT (Qwen2.5-1.5B) | 88.9% (112 of 126) |
| Desklib AI text detector | 74.6% (94 of 126) |
| Fakespot AI text detector | 81.0% (102 of 126) |
| MAGE | 66.7% (84 of 126) |
| E5-small LoRA detector | 66.7% (84 of 126) |
| OpenAI RoBERTa detector | 20.6% (26 of 126) |
| TMR (Target Mining RoBERTa) | 81.0% (102 of 126) |

## How we tested Haiku

Claude Haiku 5.5 answered the same 150 prompts as the other models, matched to the topic, genre and length of the human texts. The middle Haiku text was 277 words long, a little longer than Opus and Sonnet. We report on the 126 texts outside the calibration split.

## Results

Every detector except TMR caught Haiku more often than any other Claude model. Fast-DetectGPT caught 88.9%, Fakespot 81.0%, Desklib 74.6%, and MAGE and E5-small LoRA both 66.7%. Even the OpenAI RoBERTa detector, which misses almost all modern AI text, caught 20.6% of Haiku texts, its best result.

TMR caught 81.0%, but that number means little, because it also flags 83.3% of human writing.

If you are checking text that may come from a small, fast model, detectors have their best chance. They still miss a real share, and the false positive rates on human writing stay the same whatever model you worry about.

## Questions people ask

### Why is Claude Haiku easier to detect than Opus?

Our test does not show the cause, only that Haiku texts look more machine-like to every detector except TMR, which flags nearly everything. Fast-DetectGPT, for example, caught 88.9% of Haiku texts and 63.5% of Opus texts.

### Which AI detector is best for Claude Haiku 5.5?

Fast-DetectGPT caught the most, 88.9%, and flagged 15.9% of human texts. Desklib caught fewer, 74.6%, but flagged only 6.3% of human texts.