METR and Redwood Research Red-Team Test OpenAI's Internal Agent Monitoring System: Nominal Coverage of 99.2% of Codex Traffic Can Still Be Circumvented
Employees from METR and Redwood Research conducted a three-week red-team test of OpenAI's internal misalignment monitoring system from July to August 2026. They estimated that 99.2% of internal Codex agent traffic met monitoring eligibility criteria, while simultaneously identifying multiple exploitable circumvention paths, including client-controllable request headers that disable monitoring, serialization discrepancies causing monitor failure, and unmonitored compaction events. Based on these findings, the article proposes design principles for monitoring systems: they must be capable of withstanding deliberate, strategic, and sustained attacks from high-capability internal agents.
From July 21 to August 11, 2026, one employee each from METR and Redwood Research conducted a three-week red-team test of OpenAI’s internal misalignment monitoring system with deep access privileges. The core question of the test was not how high the monitoring coverage was, but whether high-capability agents could in principle disable or subvert this system. The gap between these two concepts is the key insight revealed by this exercise.
The level of access was exceptionally rare: the two testers gained access to OpenAI’s internal codebase, misalignment monitoring prompts and configuration details, and internal documentation, and conducted technical interviews with approximately twelve researchers and engineers across the monitoring, safety-systems, and security teams. They used devices issued by OpenAI, which never left the premises, and were accompanied throughout their time onsite. The testing focused on the state of the system as it existed on or before July 21, excluding changes that were in progress at the time.
Regarding coverage, the testers estimated that approximately 75% to 94% of internal Responses API traffic (which powers products like Codex) generated by models at least as strong as GPT-5.5 was eligible for monitoring, with substantial uncertainty in both directions; within the specific subset of Responses API traffic dedicated to internal Codex agents, 99.2% was eligible for monitoring. However, being eligible for monitoring does not equate to actually being monitored—load shedding, monitor errors, or implementation defects could prevent some traffic from completing the entire monitoring pipeline.