everyone's building multi-agent systems right now. multiple llms collaborating, checking each other's work, splitting tasks researchers tested whether this actually helps across 180 controlled configurations. matched token budgets. multiple model families. four different task domains centralized coordination improved performance by 80.8% on parallelizable tasks. on sequential reasoning tasks, every multi-agent variant made things worse by 39-70% more agents isn't better. it depends entirely on the shape of the task