Running a frontier model takes a rack of expensive accelerators and a lot of engineering. Almost nobody does it themselves. Instead you use a model provider: a company like Anthropic, OpenAI, or Google that hosts the model and exposes it over an API. Your coding tool sends text to the provider, the provider runs inference on its own hardware, and the result comes back over the wire.
What the provider actually owns
Understanding the split helps you reason about cost, privacy, and reliability:
- The weights and the hardware. The model file and the machines it runs on live with the provider, not on your laptop.
- The API contract. The provider defines the request shape, the available models, the rate limits, and the pricing.
- Uptime and versions. When the provider has an outage or retires a model version, your tool is affected, because your tool is just a client.
Why it matters when you are coding
Your harness is a thin layer sitting on top of somebody else's API. That is freeing and constraining at once. You get state-of-the-art models without owning any infrastructure, but you also inherit their latency, their pricing, and their limits. Every request leaves your machine and is processed on the provider's servers, which is worth remembering before you paste in secrets or proprietary code.
Related terms
Model
A model is the trained artifact at the centre of every AI coding tool: a large file of numbers (parameters) that, given some text, produces the most likely continuation. When people say "which model are you using," this is the thing they mean.
Read definition →Model provider request
A model provider request is a single API call to the provider carrying the messages, tools, and settings for one step. It is the atomic unit of agent work, and one turn can be many requests.
Read definition →Harness
The harness is the code wrapped around a model that builds requests, runs tools, manages context, and enforces permissions. It is the agent minus the model, and it is where most of the real engineering lives.
Read definition →