langchain/dist/agents/middleware/modelRouter.d.ts

Typescript bindings for langchain

import { AgentMiddleware } from "./types.js";
import { AgentLanguageModelLike } from "../model.js";
import { z } from "zod/v4";
import { BaseDecisionModel, ChoiceAnswer, Content, JsonValue } from "@langchain/core/decisions";
/** A model available to the router and the criterion for selecting it. */
export interface ModelChoice {
  /** A chat model, or a model string accepted by `initChatModel`. */
  model: string | AgentLanguageModelLike;
  /** Description of the tasks suited to the model. */
  criteria: JsonValue;
}
export interface ModelRouterMiddlewareConfig {
  /**
   * Named model choices, each containing a model and the criterion for
   * selecting it.
   */
  choices: Record<string, ModelChoice>;
  /** Instructions the classifier should follow when selecting a route. */
  instructions: Content;
  /** Decision model used to select a route. */
  classifier: BaseDecisionModel;
}
/**
 * Select an agent's model with a decision model's `Choice` answer (beta).
 *
 * The middleware classifies the latest human message once before an agent
 * run, stores the complete `ChoiceAnswer` in agent state as `modelRoute`, and
 * uses its selected label for every model call in the run. Keeping the
 * complete answer makes probabilities and confidence available in state and
 * traces. Classifier failures propagate and terminate the run rather than
 * silently selecting a different model.
 *
 * @example
 * ```ts
 * import { createAgent, modelRouterMiddleware } from "langchain";
 *
 * const router = modelRouterMiddleware({
 *   choices: {
 *     fast: {
 *       model: "openai:gpt-5-mini",
 *       criteria: "Simple, well-scoped tasks.",
 *     },
 *     powerful: {
 *       model: powerfulModel,
 *       criteria: "Complex tasks requiring deeper reasoning.",
 *     },
 *   },
 *   instructions: "Choose the least costly model suited to the task.",
 *   classifier,
 * });
 * const agent = createAgent({
 *   model: "openai:gpt-5-mini",
 *   middleware: [router],
 * });
 * ```
 *
 * @throws Error if `choices` is empty.
 */
export declare function modelRouterMiddleware(config: ModelRouterMiddlewareConfig): AgentMiddleware<z.ZodObject<{
  modelRoute: z.ZodOptional<z.ZodCustom<ChoiceAnswer, ChoiceAnswer>>;
}, z.core.$strip>, undefined, unknown, readonly (import("@langchain/core/tools").ServerTool | import("@langchain/core/tools").ClientTool)[], readonly []>;
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