Look It Up: Multi-bit LLM Watermarking via Codebook Search

Summary

This research proposes a codebook-based watermarking scheme that maps an n-bit payload to a longer u-bit codeword and embeds it during generation through token-level logit biasing. Experiments show near-perfect recovery for 16-24 bit payloads on 200-token generations and strong performance on 127-token generations for base models, though results are weaker on some instruction-tuned models with very short texts. The Levenshtein variant improves resilience to deletions and light paraphrasing, while insertions and stronger rewrites remain challenging.