What's the difference between the Agent API and the Model API?

They answer different needs.

• Model API: you send messages and get a model reply back, like any chat-completions API. You build the loop, the tools and the checks yourself. Billed per token at the model id you call.
• Agent API: you send a task and Cosmos does it: it plans, runs commands, edits files, uses a browser and checks its work on a cloud computer, for up to 150 steps. Billed per token at the tier each call ran on, plus computer time, actions, browser time and storage writes.

Choose the Model API if#

You already have your own agent or just need text answers.

Choose the Agent API if#

You want the work done end to end without building the tooling, and you want results such as files and test output.

Both are pay as you go from the same credit balance, and both use keys from Console › API keys (the Model API needs the models:invoke permission). See the Model API overview.