Improving Detection of Watermarked Language Models

Abstract: Watermarking has recently emerged as an effective strategy for detecting the generations of LLMs. The strength of a watermark typically depends strongly on the entropy afforded by the LLM and the set of input prompts. However, entropy can be quite limited in practice, especially for models that are post-trained, for example via instruction tuning or reinforcement learning from human feedback (RLHF), which makes detection based on watermarking alone challenging. In this work, we investigate whether detection can be improved by combining watermark detectors with non-watermark ones. We explore a number of hybrid schemes that combine the two, observing performance gains over either class of detector under a wide range of experimental conditions.