import type { CompletionRequest } from '../../types/messages.js';
import type { AgentMiddleware, AgentMiddlewareContext, AgentModelClient } from '../create-agent.js';
/** A model to fall back to: a model name for the agent's own client, or another client. */
export type ModelFallbackTarget = string | {
    client: AgentModelClient;
    model?: string;
};
/** One fallback about to happen. */
export interface ModelFallbackEvent {
    /** The model that failed. */
    from: string;
    /** The model tried next. */
    to: string;
    /** What the failed call threw. */
    error: unknown;
}
/** Options for `modelFallback()`. */
export interface ModelFallbackOptions {
    /** Whether an error moves on to the next model. Defaults to every error but a cancellation. */
    fallbackOn?: (error: unknown, model: string) => boolean;
    /** Called before each fallback, for logs and metrics. */
    onFallback?: (event: ModelFallbackEvent) => void;
}
/**
 * Tries other models, in order, when the model call fails.
 *
 * The client's router already falls back between providers for one request; this is the fallback
 * it cannot make: to a client of a different kind, or once the client's own routes are exhausted. A
 * target with its own client is called through `complete()`, never streamed, and middleware after
 * this one does not wrap it.
 */
export declare function modelFallback(models: readonly ModelFallbackTarget[], options?: ModelFallbackOptions): AgentMiddleware;
/** What `dynamicModel()` decides from: the step's context and the request about to be sent. */
export type DynamicModelContext = AgentMiddlewareContext & {
    request: CompletionRequest;
};
/**
 * Chooses the model for each call from the run so far.
 *
 * A cheap model for the first steps and a stronger one once the task proves hard, a model with a
 * longer context once the transcript grows, or a tenant's own model. Returning nothing keeps the
 * model the request already names.
 *
 * ```ts
 * dynamicModel(({ state }) => (state.iterations >= 4 ? 'gpt-5' : 'gpt-5-mini'))
 * ```
 */
export declare function dynamicModel(select: (context: DynamicModelContext) => string | undefined | Promise<string | undefined>): AgentMiddleware;