A/B testing de prompt em produção

import { Statsig } from 'statsig-node';
await Statsig.initialize(process.env.STATSIG_SECRET!);

export async function generateResponse(user: User, query: string) {
  const variant = await Statsig.getExperiment(user, 'assistant_prompt_v2');
  const promptVersion = variant.get('version', 'v1');

  const systemPrompt = promptVersion === 'v2' ? PROMPT_V2 : PROMPT_V1;
  const start = Date.now();
  const response = await claude.messages.create({
    model: 'claude-sonnet-4',
    system: systemPrompt,
    messages: [{ role: 'user', content: query }],
  });

  // Log metrics
  await Statsig.logEvent(user, 'llm_request', {
    variant: promptVersion,
    latency_ms: Date.now() - start,
    input_tokens: response.usage.input_tokens,
    output_tokens: response.usage.output_tokens,
  });

  return response;
}