TextSeal2: Distortion-Free LLM Watermarking with Copula Mixing and Memoryless Races

Summary

TextSeal2 is a distortion-free watermark for LLMs that keeps its signal under speculative decoding, with tokens replacing rejected drafts still watermarked and the acceptance rate unchanged. It merges two or more keys into one virtual key coupled to fresh noise via AutoMark's Gaussian copula, and evaluated on three LLMs it detects 8 to 22 percentage points more 100-token answers than TextSeal at a false-positive rate of $10^{-3}$. Under speculative decoding it detects 18 and 22 percentage points more 200-token answers than TextSeal and textGrain, respectively, at the same acceptance rate.