| Who does the work | Certified engineers, or engineers who shipped inside Meta, Spotify, UBS and Starling Bank. Senior, hands-on, no bench of juniors. | A partner sells it; a large mixed-seniority team delivers it. | People you brief, manage and direct yourself. | Advisers who hand the build to somebody else. |
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| Time to first production slice | Typically weeks. One real workflow, end to end, in your environment. | Months, after a discovery phase and a mobilisation phase. | As fast as the plan you give them, and no faster. | None. The output is a document. |
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| Model choice | From production evidence across OpenAI, Anthropic, Gemini and open-source, not from a vendor deal. | Usually shaped by the vendor alliance and reseller economics the firm already has. | Whatever the people you hired happen to know. | A recommendation, with nothing in production behind it. |
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| Governance | Built as platform controls: default-deny access, permission-aware context, deterministic checks, human approval, evaluation gates in CI. | A governance workstream, usually a policy set and a steering committee. | Yours to define, enforce and audit. | A framework for somebody else to implement. |
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| What you are left with | Running systems, the architecture written down, and a team that can extend both. | A system your team did not build, and a change-request route into it. | Whatever got built. The knowledge leaves when they do. | A roadmap, and the build still to buy. |
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| Commercial shape | Fixed-scope statements of work, a retained architecture engagement, or embedded engineers from three months. One supplier, one contract. | Multi-phase programme against a rate card. | Priced per person, per day, open-ended. | Fixed fee for the report. |
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