PACT: Emergent Institutions in Long-Horizon Multi-Agent Coding Systems

As autonomous agents become more widely deployed, coordinating access to shared computing resources and services will become increasingly important. Recent incidents have already revealed unplanned coordination and resource sharing between agents, highlighting the safety implications of these interactions. Yet prior studies of agent negotiation often use stylized games and simulated bargaining, leaving open how these behaviors develop during sustained, long-horizon programming work. We propose PACT Programming Agents Contending for Time a framework in which agents solve sequences of programming tasks under individual deadlines while negotiating access to a shared execution resource. Their agreements determine when and for how long they can inspect programs, compile code, and run tests. Furthermore, we develop a 21-category taxonomy of negotiation strategies and emergent norms and use it to analyze eight models and audit more than 1,500 trajectories across different environmental settings. We find that agents spontaneously develop informal institutions: persistent rules and commitments grounded in reputation, reciprocity, and precedent. These arrangements carry across tasks and influence resource allocation, with agents sometimes foregoing immediate advantages to honor earlier agreements. Among the models tested, newer frontier models exhibit more relational behavior than older or lightweight models. Alongside cooperation, we observe exclusionary coalitions and rare divide-and-conquer strategies. PACT provides a controlled setting for proactively and systematically auditing how these relationships emerge, shape access to resources, and affect the safety and coordination of multi-agent systems.