Choose a model

Thermite’s agents need an AI model to think with. The judge does not: it measures changes with no model at all. This page helps you pick a model and points you to the guide that connects it.

Try the options in this order. Each one costs more, or needs more set-up, than the one before.

Option	Costs	You need	Runs in
OpenCode’s free models	Nothing	Nothing	OpenCode v2 only
A model server on your computer	Nothing but your hardware	A server such as Ollama, vLLM or LiteLLM	Pi or OpenCode v2; Codex when the server answers `/responses`
An API key	The provider’s prices	A key from an OpenAI-compatible provider or from Anthropic	Pi or OpenCode v2; Codex for OpenAI’s own API
A subscription	Your plan, nothing more	A Claude Pro or Max plan, or a ChatGPT Plus or Pro plan	Claude: Claude Code only. ChatGPT: Pi, OpenCode v2 or Codex

You connect every option on one dashboard page, Settings › Providers, and then give a rig one of its models. Connect a model provider shows how.

Nothing stops research by default: agents keep working until the job is done or you stop them. Before agents use a paid API key:

Give each campaign a stop time: Stop after (hours) under Advanced on the New campaign page, or budget.wall_hours in the contract. It works on every rig.
Set a spending limit at the provider, on the key or the account, if the provider has one.
Watch the spend, and Pause the run if it goes too fast (Steer a run).

Thermite’s money limits count less than their names suggest. The contract’s budget.llm_usd counts only on a rig that has token prices (THERMITE_LLM_USD_PER_MTOK_IN and THERMITE_LLM_USD_PER_MTOK_OUT). The local stack can set them; rigs that control sets up on machines and clusters, or by a join command, can’t have them yet. It counts only the workers’ trials (their working sessions), not the planner or the advisors. The advisors’ daily limit, max_usd_per_day, counts only the openai runtimes in the advisors file that have prices: an advisor given its model on Edit rig counts as $0. See Set a budget or a stop time and goal 061.

A subscription never buys more: at its limit, the agents wait.

What every model must do

The model must support tool calling. Workers act only through tools: they read and edit code, run commands and submit their changes with them. A model that only writes text cannot do that work.

The rig’s Model route check tests exactly this. It sends one short request and passes only when the model answers with a correct tool call. The rig runs it by itself each time control gives it a new model. See Check a rig.

Where the agents run

Each agent runs inside a program that gives the model its tools: the worker harness. (The harness alone is something else: the rig’s container that holds the judge and the agents.) You choose the worker harness in the block Harness and model for each rig on Settings › Providers, in the Runs in column on a rig’s Edit rig page, or under The agents run in when you choose the agents’ model on the New campaign page:

Pi: Thermite’s own built-in agent. It is the default.
OpenCode v2: the OpenCode coding agent, which is always in Thermite’s harness image.
Claude Code: Anthropic’s own program. It is in the image only when the image is built with it, and it runs only with a Claude subscription.
Codex: the Codex CLI, OpenAI’s own coding agent. It is in Thermite’s published harness images, and it runs with a ChatGPT subscription or an OpenAI-compatible provider whose server answers OpenAI’s Responses API (/responses), as OpenAI’s own API does. The planner follows the workers into Codex unless it has a model of its own.

Not every model works in every worker harness. Thermite refuses these pairings when you save them:

You choose	The dashboard says
Claude Code with any provider other than a Claude subscription	“Claude Code runs only with a Claude subscription here: choose Pi or OpenCode v2 for this provider.”
OpenCode’s own models in Pi	“OpenCode’s free models run only in the OpenCode harness: choose OpenCode v2 for this rig.”
Codex with an Anthropic or OpenCode provider	“Codex runs only with a ChatGPT subscription or an OpenAI-compatible provider: choose Pi or OpenCode v2 for this provider.”
OpenCode’s own models for an advisor	“The role cannot use OpenCode’s own models: they run only in OpenCode. Choose another model.”

A Claude subscription always runs in Claude Code: when you choose one of its models, Thermite picks Claude Code for you. A ChatGPT subscription runs in Pi unless you choose OpenCode v2 or Codex.

1. OpenCode’s free models

OpenCode runs a service with some free models. They need no key and no account. This is the quickest way to watch agents work.

On Settings › Providers, add a provider of the type OpenCode (its own models) and leave Base URL and API key empty.
Give the rig one of its models whose name ends in -free, with the worker harness OpenCode v2. Those are the ones OpenCode serves without a key.

OpenCode decides which of its models are free, and the list can change. Its list also names models it does not serve, and it limits free use: a check that fails with Rate limit exceeded may pass a few minutes later. If the model check fails, try again later or try another model (what the failures mean). The tutorial Hand the work to agents walks through this path from start to end.

2. A model server on your own computer

A model server that you run yourself, such as Ollama, vLLM or LiteLLM, costs nothing per request. Add it as an OpenAI-compatible provider:

Base URL: the server’s address, ending in /v1. Thermite runs in containers, and inside a container localhost is the container itself. Use host.docker.internal instead, for example http://host.docker.internal:8000/v1. With Podman, host.containers.internal works too.
API key: Thermite asks every new OpenAI-compatible provider for a key. If your server checks none, type any word without spaces.

Control reads the server’s model list from where control runs, and each rig calls the model from where the rig runs, so both must reach the address. On the local stack, control and the harness container both reach host.docker.internal.

A rig on a cluster can’t use a server on a private address. In a namespace that control creates, or that you join, the rig’s harness container reaches only DNS and addresses outside the private ranges (Add a rig on a cluster). Give such a rig a hosted provider instead.

3. An API key from a provider

Use a key from a hosted provider:

OpenAI-compatible covers most services and gateways, for example OpenRouter or LiteLLM. Enter the provider’s base URL, ending in /v1, and your key.
Anthropic is Anthropic’s own API. Leave Base URL empty and enter your key.

Control seals each key as soon as you save it, never shows it again, and gives it only to the rigs that use one of the provider’s models. Set a stop time and a limit at the provider first, as the caution above says.

4. A Claude or ChatGPT subscription

If you already pay for a Claude or ChatGPT plan, its agents can work on that plan:

Claude subscription (Pro or Max): you paste a token from claude setup-token. Its models run only in Claude Code, so the harness image must be built with Claude Code. See Use a Claude subscription.
ChatGPT subscription (Plus or Pro): you sign in with ChatGPT from the dashboard. Its models run in Pi, OpenCode v2 or Codex. See Use a ChatGPT subscription.

A subscription is for your own Thermite only. A Thermite that several people use takes API keys. When a plan’s usage is full, the agents wait for it; nothing pays for more.

Mix models

You can give each agent its own model: the workers one, the planner another, and each advisor a third. For example, a free or local model for the workers, and a stronger model for the planner. See Give each agent its own model.

A rig can also take its model from its own settings, the THERMITE_MODEL_* variables, instead of from control. Connect a model provider explains when that helps.