AgentTrace: Execution-Level Fingerprinting of Black-Box LLM Agents

Summary

AgentTrace is an active framework that identifies the foundation model behind a black-box LLM agent from observable execution traces. It injects structurally ambiguous probes that trigger tokenization-sensitive serialization failures at rigid tool interfaces, then models the sequence of repair operations with lightweight Markov chains. The method reaches 96.0% attribution accuracy under adversarial identity spoofing and separates intra-family variants that share tokenizers, such as Llama-3 8B and 70B.