Antimatter

PUT/v1/agents/{id}/definitionAPI key

Hosted agent runs (lib/agent-runs.ts): the agent's definition runs a loop on the server, model call and tool calls, each step a job of its own. Every model call is a request by the agent's own key, billed to its wallet under its policy. Needs the agents scope; an agent's own key is refused. A 404 while hosted runs are off on the deployment.

Parameters

Path and query parameters
Field	Type	What it is
id (path)required	string	The agent's id; self on an agent's own key.

Request body

application/json, required

Request body fields
Field	Type	What it is
modelrequired	string	A model id or an autopilot id on the agent's own list.
instructions	string or null	At most 32000 characters.
tools	array of object
tools[].typerequired	string	One of "function", "code_interpreter", "mcp", "image_generation", "memory", "antimatter_tools", "x402_fetch", "file_search", "studio".
tools[].language	string	code_interpreter only. Read back on every code_interpreter entry. One of "javascript", "python".
tools[].vector_store_ids	array of string	file_search only: vs_ ids the agent's key can reach.
temperature	number or null	From 0 to 2.
max_output_tokens	integer or null
limits	object
limits.max_steps	integer or null	Model calls and tool batches, together.
limits.max_wall_seconds	integer or null	Wall clock from the run's creation.
limits.max_cost_micros	integer or null	What the run's model and image calls may be billed, in micro USD.

Example

{
  "model": "antimatter/auto"
}

Answer 200

Replaced.

Fields of the 200 answer
Field	Type	What it is
object	string	One of "agent.definition".
agent_id	integer
model	string
instructions	string or null
tools	array of object
temperature	number or null
max_output_tokens	integer or null
limits	object	What a run gets when it asks for none, the deployment's caps applied.
limits.max_steps	integer
limits.max_wall_seconds	integer
limits.max_cost_micros	integer
updated	integer	Unix seconds.

Answer 201

Stored for the first time.

Fields of the 201 answer
Field	Type	What it is
object	string	One of "agent.definition".
agent_id	integer
model	string
instructions	string or null
tools	array of object
temperature	number or null
max_output_tokens	integer or null
limits	object	What a run gets when it asks for none, the deployment's caps applied.
limits.max_steps	integer
limits.max_wall_seconds	integer
limits.max_cost_micros	integer
updated	integer	Unix seconds.

Errors

400OpenAI shaped error.
401OpenAI shaped error.
403OpenAI shaped error.
404OpenAI shaped error.

Every error answers in one shape, with its type, code and the field it names. The whole list is in the docs' Errors section.

Try it

The same call with curl

curl -X PUT https://useantimatter.com/v1/agents/{id}/definition \
  -H "Authorization: Bearer $ANTIMATTER_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"model":"antimatter/auto"}'