AI Text Watermarking May Not Be Able to Meet the E.U.'S New Rules

Tests of OpenAI's textGrain watermark, released in October to comply with the E.U. AI Act's transparency obligations, show detection falls to about 80% for 200-token texts versus 95% for 400-token texts, and replacing 25% of words with synonyms cuts detection from 92% to 17%. The E.U. Code of Practice does not require watermarks on outputs shorter than 200 tokens, and with no measurable legal thresholds and no peer-reviewed evaluation yet, it is too early to say whether textGrain meets the requirements. OpenAI says textGrain matched or outperformed Google's SynthID Text in its own unverified tests, and researchers including Cornell's John Thickstun and KInIT's Dominik Macko have only just gained access to evaluate it.