export declare const FAST_MODE_BETA = "fast-mode-2026-02-01";
export interface BetaHeaderOptions {
    oauthEntries?: readonly string[];
    effort?: boolean;
    extendedCacheTtl?: boolean;
    fast?: boolean;
    effortEntry: string;
    extendedCacheEntry: string;
}
export declare function composeBetaHeader(options: BetaHeaderOptions): string | undefined;