/**
 * Latency histogram — tracks per-model request durations with percentile support.
 * Uses a fixed-size ring buffer per model to bound memory.
 */
/**
 * Record a request duration for a model.
 */
export declare function recordLatency(model: string, durationMs: number): void;
export interface LatencyStats {
    count: number;
    min: number;
    max: number;
    mean: number;
    p50: number;
    p90: number;
    p95: number;
    p99: number;
}
/**
 * Compute latency percentiles for a model.
 */
export declare function getLatencyStats(model: string): LatencyStats | null;
/**
 * Get stats for all models.
 */
export declare function getAllLatencyStats(): Record<string, LatencyStats>;
/**
 * Format latency stats for display.
 */
export declare function formatLatencyStats(stats: Record<string, LatencyStats>): string;
/**
 * Reset all samples (for testing).
 */
export declare function resetLatency(): void;
