Asynchronous monitoring, incident investigations, and compliance audits assume agent traces are a faithful record. We tested whether local LLM agents in harnesses including Claude Code, Codex, Antigravity, Open Code, and Grok Build can tamper with their own traces. All tested harnesses except Muse Code let agents delete traces when asked, without monitor guardrails firing.
The gap is exploitable: external instructions can induce trace deletion. More concerning, frontier models will naturally discover trace tampering when optimizing for reward, and in multi-agent settings they copy tampering from peer examples. This means trace integrity cannot be assumed in current agent infrastructure.