OpenAI Launches AI Watermarking for ChatGPT in EU, But Detection Remains Vulnerable to Simple Edits

Reviewed byNidhi Govil

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OpenAI will watermark ChatGPT and Codex outputs in the European Union to comply with the EU AI Act's transparency requirements. The company's textGrain method achieves 92% detection in tests, but editing just 10% of the text drops accuracy to 66%. Unlike rival Anthropic, OpenAI keeps watermarking off by default outside Europe.

OpenAI Deploys AI Watermarking to Meet EU AI Act Requirements

OpenAI announced it will automatically watermark text generated by ChatGPT and Codex for users in the European Union, marking a significant step toward compliance with the EU AI Act

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. The transparency rules, which took effect on August 2, require AI companies to mark AI-generated content in ways other systems can identify

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. The invisible watermark will roll out over the coming weeks to eligible ChatGPT and Codex users on all plans within the European Union

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. Outside the EU, the AI text watermarking feature remains off by default, though developers using OpenAI's API anywhere in the world can activate it for select models

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Source: Gadgets 360

Source: Gadgets 360

How textGrain Creates Detectable AI-Generated Content

OpenAI's proprietary method, called textGrain, works by adding an invisible statistical signal to the model's word choices

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. The watermark subtly shapes word selections, leaving patterns human readers cannot see but specialized detectors can identify using a secret key

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. Co-written with researchers from the University of Pennsylvania and Yale, OpenAI published a technical paper explaining how large language models predict word tokens one at a time from a probability distribution, and by periodically selecting different words—ideally synonyms—the resulting text deviates from the statistical pattern produced by an unbiased model output

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. Because the watermark lives in the words themselves, it travels with the text when copied and pasted

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. OpenAI claims textGrain matched or exceeded other approaches like Google DeepMind's SynthID for text, which forms the basis for watermarking that Anthropic announced in August

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Source: Gizmodo

Source: Gizmodo

Detection Accuracy Drops Sharply With Minor Text Modifications

While OpenAI's best-case tests show a 92% successful detection rate, the system's vulnerability to simple editing raises questions about its practical effectiveness for compliance with the EU AI Act

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. Changing just 10% of the text in ChatGPT outputs reduces successful detection by almost 30 percentage points—from 92% to 66%

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. Replacing 20% of words with synonym substitution can lower the success rate by almost 75%, and when 25% of words are swapped, the watermark signal could only be detected in 17% of cases

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. Detection rates are also lower for shorter passages, with 200-word texts flagged only 80% of the time compared to 95% for 400-word passages

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. The results are worse in functional texts involving math or code, where substitutions are more likely to introduce errors

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Limited Detector Access and Cautious Rollout Strategy

OpenAI will provide access to AI detectors only to a limited number of researchers and expert organizations, with a request-for-approval process for others to be added over time

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. The company stated these limitations contribute to its decision to restrict initial detector access, allowing approved parties to evaluate reliability and responsible uses

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. OpenAI cautioned that a missing watermark does not prove human authorship, as the text could be too short, too heavily edited, or generated by another company's generative AI system

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. The company emphasized that watermarks can indicate an OpenAI system generated or processed part of a passage, but not how much human judgment, editing, or creativity went into it

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. OpenAI argues its regional approach gives the company room to learn from real-world use and feedback

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Diverging Approaches: OpenAI Versus Anthropic on Global Implementation

Unlike Anthropic, which enabled machine-readable watermarking globally in August, OpenAI is currently making the invisible watermark default only where regulators require it

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. Anthropic's decision to watermark text generated by Claude worldwide drew backlash from some users who argued they had supplied the instructions, context, and decisions while Claude was just the tool

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. Anthropic explained it applied watermarking globally because it doesn't yet have a durable way to scope it by region, citing the EU regulation's mention of preventing potential circumvention

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. OpenAI had previously built a text watermark but held off on releasing it, partly over concerns that users would switch to rivals that didn't watermark, The Wall Street Journal reported in 2024

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. Both Anthropic and OpenAI are among the companies—including Google, Meta, and Microsoft—that have committed to following the European Union's code of practice on AI-generated content

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