Session-Bound Behavioral Watermarking for Autonomous LLM Agents

Summary

AgentAnchor is a session-keyed behavioral watermark for attributing LLM agent trajectory logs to their owner. Each step key derives from a secret key, a fresh public session identifier, and semantic states of recent observations, and parity evidence is embedded through a KL-bounded exponential tilt. The authors formulate a learned-forgery threat, in which repeated observation of watermarked trajectories enables cross-session forgery through learned action preferences.