Spine-Branch Coordination Cuts Multi-Agent Computer-Use Cost 34-70% by Never Merging VM State

arXiv 2608.22077·medium signalXBlueskyLinkedInCopy link

Multi-agent computer use hits a physical bottleneck that prior systems handled ad hoc: the state of two virtual machines cannot be merged. Spine-Branch decomposes a task into a graph where the spine carries the main flow with continuous VM state and branch VMs run in parallel only to collect information the spine needs, then get discarded, so no merge ever happens. On 200 long-horizon tasks from Odysseys across three computer-use backbones it improved success rate by 6.0 to 16.5 points while reducing per-task cost by 34% to 70%.