Hire an OpenAI API developer without the freelancer hunt

Most OpenAI API projects begin with a quick prototype that works on the developer's laptop and then struggles in production: 429 errors at busy hours, outputs that break a parser one time in fifty, and a monthly bill nobody predicted. The fixes are well understood. Requests get exponential backoff with jitter, outputs are constrained with structured outputs against a JSON schema, and long, repeated instructions sit at the start of the prompt where automatic prompt caching can reuse them.

Function calling, or tool use, lets the model request actions in your system such as looking up an order, while your code decides whether to run them. The agent writes those tools with strict argument schemas and permission checks, so the model can never call something it shouldn't. Work that doesn't need an instant answer, like tagging a backlog or summarising last week's records, moves to the Batch API, which runs at a lower price in exchange for results within a day.

OpenAI has announced it is retiring the Assistants API in favour of the Responses API, and many teams need their threads, files and tools moved across. The migration keeps your behaviour the same while switching endpoints, with before-and-after tests on real examples. Keys are created as project keys in your organisation, with spending limits and usage alerts set there, and you own the account, the billing and any data retention settings.