Will we own the backend code and API contract?

Yes, completely. Source code ownership and IP transfer terms are agreed in writing before kick off, the NDA is signed before any project discussions, and the repository is yours from commit one. The OpenAPI spec or GraphQL schema is yours. There are no surprise licence fees later, no usage limits, no white labelled dependencies that lock you in. You can take the backend to any team, any agency, or your own in house engineers.