# Feature-Flag → Cost-Flag: Engineering-Level Measurement of A/B Test's Real $/User Impact

> Source: https://sukruyusufkaya.com/en/learn/token-ekonomisi/feature-flag-cost-flag-ab-test-llm
> Updated: 2026-05-14T14:44:12.293Z
> Category: Token Ekonomisi & LLM Cost Optimization
> Module: Module 4: Cost Attribution
**TLDR:** You want to show a new AI feature to 50% of users to measure impact. Conversion is easy to measure — but the cost difference? This lesson covers adding a cost-flag to each A/B variant, statistical significance, and decision-making with LTV.