Short answer: building a multi-agent prototype directly on a model provider's API is genuinely fast — a working demo in a weekend is realistic. The gap is everything between "it works in the demo" and "it's safe to leave running unattended in production," which is where most in-house builds stall.
The part that's actually easy
Calling a model, handling a tool call, chaining a couple of steps together — every major model provider's API makes this straightforward, and a team with reasonable engineering skill can have something that looks like a working multi-agent system running in days, not months. This isn't a strawman: it's the normal, correct first step, and building it in-house is a completely reasonable way to validate whether multi-agent is the right shape for a problem at all.
The part that isn't
The infrastructure gap shows up once that prototype needs to run for real: session management that survives a process restart, SSE streaming instead of blocking request/response, routing logic that's checked against something rather than trusted to a prompt, a durable record of what happened in a given run for when something goes wrong, and a hard limit on how deep and how expensive a chain of agent-to-agent calls can get before it's stopped.
None of these are individually hard engineering problems. Collectively, they're the reason "the prototype works" and "this is production-ready" are different milestones, often separated by months of work that isn't specific to the product being built — it's the same plumbing any team building multi-agent systems eventually needs.
What a managed platform actually removes from that list
Anter's orchestrator ships validated routing (write-time allowlist plus runtime existence check on every handoff), durable atomic persistence of every routing event, SSE streaming with resumable replay, fail-closed unattended approvals, and bounded agent-to-agent chains — as the default runtime behavior, not infrastructure a team builds and maintains themselves. The trade-off is real: it's a managed platform, not source code you own outright. For a team whose actual product isn't agent infrastructure, that trade-off is usually the right one.
See the full side-by-side comparison for how this stacks up against Claude Managed Agents, OpenAI AgentKit, CrewAI, and Base44 specifically.