A subagent's model is not the main model

I have a small lab app that runs three Claude Agent SDK agents, each with its own job. A settings page picks the model for each agent. I set one of them to Opus, started a run, and the sessions table still said “sonnet”. There was no error.

The setting went into the agent’s AgentDefinition:

const agents = {
  "my-agent": { description, prompt, tools, model: settings.model },
};

AgentDefinition.model applies when the main agent starts that definition as a subagent. My app calls query() with the agent’s prompt directly, so the main loop ran, and the main loop takes its model from options.model, which I hadn’t set. The fix was to pass it there too:

for await (const msg of query({
  prompt,
  options: { model: agent.model, agents },
})) {
  // ...
}

The table still said “sonnet” after that, and that was a second bug. The API route that queued the run wrote a hardcoded model: "sonnet" into the session row, so the table never showed the setting anyway.

A column like that stores the model you asked for. To see the model that ran, read model from the SDK’s init message, or modelUsage from the result message.