The case for multi-agent systems is compelling. Complex tasks can be decomposed into parallel workstreams. Specialized agents outperform generalists on their specific domains. Orchestration allows capabilities to be combined in ways no single agent could achieve. The whole is greater than the sum of its parts.

The case against rushing into multi-agent systems is equally compelling, and less often made. Every agent you add is another source of variance, another failure mode, another system whose behavior you need to understand and test. In a single-agent system, a failure has one origin. In a multi-agent system, a failure can originate anywhere, propagate through handoffs in non-obvious ways, and arrive at the output looking like something completely different from what caused it.

The handoff problem is particular to multi-agent architectures and particularly insidious. Agent A produces output that looks correct. Agent B receives it, interprets it slightly differently than Agent A intended, and produces output that reflects that misinterpretation. Agent C receives Agent B's output, makes a reasonable inference from it, and the final result is confidently wrong in a way that traces back to a subtle semantic slip three steps earlier. Each agent did its job. The system failed.

This argues not against multi-agent systems, but for building them incrementally. Start with the single-agent version, even if you know it won't scale to the full problem. Understand its failure modes. Then decompose one piece at a time, validating each handoff explicitly before adding the next agent. The teams that design the full multi-agent architecture upfront and build it all at once accumulate technical debt they can't see until the whole thing is running.

Observability becomes non-negotiable at multi-agent scale. You need to be able to trace a final output back through every agent that contributed to it, with the full context and reasoning at each step. Without that, debugging a multi-agent failure is guesswork.

More agents means more capability. It also means more places to lose the thread.