Use Model directly

Use Model directly when you need a single model call or want to control tool execution yourself.

Get a complete reply

This example uses the environment variables and runner from the quickstart:

import { Model, OpenAIProvider, SystemMessage, UserMessage } from "@yong_xie/lighter";

const model = new Model(new OpenAIProvider(
  process.env.OPENAI_API_KEY!,
  process.env.OPENAI_MODEL!,
));

try {
  const message = await model.invoke({
    // Model does not add a system prompt; include one when needed.
    messages: [
      new SystemMessage("You are a bookstore advisor. Keep your answers brief."),
      new UserMessage("Name a bookstore on the moon."),
    ],
  });
  console.log(message.content);
} catch (error) {
  // Model throws errors directly instead of returning an AgentResponse with status.
  console.error("Model call failed:", error);
  process.exitCode = 1;
}

invoke() returns one AssistantMessage. If the model requests tools, the calls are in toolCalls. Model does not execute tools or start another round automatically.

Stream a reply

import { Model, OpenAIProvider, UserMessage } from "@yong_xie/lighter";

const model = new Model(new OpenAIProvider(
  process.env.OPENAI_API_KEY!,
  process.env.OPENAI_MODEL!,
));

try {
  for await (const event of model.stream({ messages: [new UserMessage("Hello!")] })) {
    if (event.type === "text_delta") {
      process.stdout.write(event.text);
    } else if (event.type === "message") {
      // Unlike Agent, Model yields the complete message event directly.
      console.log("\nComplete message:", event.message);
    }
  }
} catch (error) {
  console.error("Streaming failed:", error);
  process.exitCode = 1;
}

Model streams text_delta, reasoning_delta, and message events. It does not yield a final AgentResponse.

Tools and hooks

Pass tool.getSpec() in the request’s toolSpecs to describe tools to the model. After receiving a call, your application handles parameter parsing, execution, and the next request. Use Agent to automate these steps.

The second argument of invoke(request, hooks?) and stream(request, hooks?) accepts beforeModel and afterModel, just like Agent’s model hooks. Calling a Provider directly bypasses these hooks.