The honest framing is not in-house versus agency forever — it is who does the first one. The first workflow is where most of the expensive mistakes are available: over-scoping, missing permissions design, no baseline to measure against, no owner for exceptions.
What actually decides it is capacity, not capability
Most teams that choose in-house are capable of the work. What stalls them is that the automation project sits behind the product roadmap, and a workflow that is everybody's second priority takes three quarters instead of three weeks. If your engineers are already fully committed, the in-house option is not cheaper — it is simply later.
Whichever you choose, insist on ownership
An external build should leave you with the workflow definitions, the credentials, the runbook and a named internal owner. If a partner's proposal has no handover in it, you are not buying a system, you are renting a dependency. The same test applies internally: a workflow that only one engineer understands has the same bus factor as an agency you cannot reach.
For the criteria to apply once you have decided to bring someone in, see our guide on choosing an AI automation agency.