[key: string]:
  | undefined
  | MetricValueType
| () => Record<string, MetricValueType | undefined>

new LlmMetrics(options: LlmMetricsOptions): LlmMetrics;

optional durationNs: number;

optional numInputTokens: number;

optional numOutputTokens: number;

optional numTotalTokens: number;

optional timeToFirstTokenNs: number;

toJSON(): Record<string, MetricValueType | undefined>;