Who Is Behind the Harness? Fingerprinting LLMs through Agentic Behavior
LLMs increasingly operate through coding-agent harnesses that inspect repositories, invoke tools, and modify files. Substituting the model behind such an agent can therefore change security-relevant decisions, including whether it verifies changes or recovers safely from failures. Existing LLM fingerprints largely infer identity from direct text or token distributions. In coding agents, these signals are mediated by system instructions, controller logic, tools, and execution feedback, limiting their transfer. We present LIDAR (LLM Identification from Decisions and Actions at Runtime), an active black-box fingerprinting method for coding-agent execution. Three coding probe pairs expose pos...
| Authors | Chuyi Wang, Xiaohui Xie, Tongze Wang et al. |
|---|---|
| Primary category | cs.CR |
| Published | 23 September 2026 |
| Last updated at source | 23 September 2026 |
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