# OpenAI’s textGrain watermark fails EU tests on short or edited text

Digest AI · Policy & Regulation · published 2026-11-05T15:00:03Z

Canonical: https://digestai.news/story/openais-textgrain-watermark-fails-eu-tests-on-short-or-edited-text

## Summary

The EU’s AI Act requires AI-generated text to be watermarked for transparency, but OpenAI’s new **textGrain** system—designed to comply—struggles in real-world use. Tests show detection rates drop sharply for texts under 150 words or after editing, with synonym replacement cutting accuracy from 92% to 17%. OpenAI claims textGrain outperforms Google’s **SynthID Text** in its own tests, but those results lack independent verification. The EU’s rules demand watermarks be *effective* and *robust*, yet no clear benchmarks exist for what constitutes compliance. Critics like **Thomas Souverain** argue the system may not meet legal standards, risking fines of up to 7% of OpenAI’s revenue if found non-compliant. OpenAI has not responded to requests for comment, and its collaboration with researchers—including **John Thickstun** and the **Kempelen Institute**—remains in early stages. Souverain calls for open-sourcing textGrain to allow broader scrutiny, citing Meta’s **SynthID** as a model for transparency.

## Key points

- OpenAI’s textGrain watermark detects AI-generated text at 95% accuracy for 400-token passages but drops to 80% for 200 tokens
- Editing text reduces detection rates: replacing 10% of words cuts accuracy from 92% to 66%
- EU AI Act lacks measurable thresholds for watermark effectiveness, leaving compliance uncertain

## Why it matters

If textGrain fails EU scrutiny, OpenAI could face fines and reputational damage, while competitors gain an edge. For users, unreliable watermarks undermine trust in AI-generated content’s traceability, complicating compliance with emerging transparency laws.

## Sources

1. [AI Text Watermarking May Not Be Able to Meet the EU’s New Rules](https://spectrum.ieee.org/ai-watermark-openai-textgrain-europe) (IEEE Spectrum AI, 2026-11-05)

## Cite

Digest AI, "OpenAI’s textGrain watermark fails EU tests on short or edited text", 5 November 2026, https://digestai.news/story/openais-textgrain-watermark-fails-eu-tests-on-short-or-edited-text

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