Study: AI agent teams cost 1.8–5.1x more for little quality gain
Evals company Vals AI tested GPT-6 Sol and Claude Opus 5.5 on its Vibe Code Bench both as single agents and as agent teams, at medium and maximum reasoning effort. Teams cost between 1.8x and 5.1x more than single agents, yet only one of four comparisons showed a statistically significant improvement: GPT-6 Sol at medium reasoning, where the team scored 7.3 points higher; at maximum reasoning, neither Sol's nor Opus 5.5's team gained a real advantage. The report also notes that in two of Anthropic's own tests with Opus 5.5, quality gains shrank as more agents were added, while OpenAI researcher Noam Brown has said multi-agent systems mainly buy speed rather than better quality.
If agent teams mostly buy speed at multiples of the token cost, many tasks may be better served by one agent with a higher reasoning budget.