Agents

A model, its instructions, and what it may do, declared once and resolved for each person.

An agent is a model, its instructions, and what it's allowed to do. You declare it with defineAgent and give it a name; clients pick it by that name.

Why it exists

The AI SDK's agent is an object you build per call. In a product, the same agent serves thousands of people, and what it may do often depends on who they are: a different model on the paid plan, a tool only admins get. defineAgent describes the agent once, and Latch builds it for each turn, for that person.

The smallest version

ts
import { defineAgent } from "@intentface/latch-core";

const support = defineAgent({
  model: anthropic("claude-sonnet-4-6"),
  instructions: "You help customers with their orders.",
  tools: { find_order, refund },
  toolApproval: { refund: "user-approval" },
});

When it depends on the caller, pass a function instead:

ts
const assistant = defineAgent<Principal, Ctx>(({ context }) => ({
  model: context.plan === "pro" ? anthropic("claude-sonnet-4-6") : anthropic("claude-haiku-4-5"),
  instructions: `You work for ${context.orgName}.`,
}));

What an agent can have

  • Params: what its chats are about, such as a ticket or a document, given once when a chat starts. See Principal, context and params.
  • Tools, some of them behind approval.
  • Connections to other services, by name (connections: ["linear"]).
  • Subagents it can hand work to (subagents: ["researcher"]).
  • Built-in tools you switch on: fetching web pages, asking the user a question, managing their schedules, a workspace with files and a shell.
  • Agents stored in a database instead of code, so users can create their own, with versions you can test before they go live.

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