Most founders building on top of LLMs are shocked by their first big invoice. The unit economics of AI products are fundamentally different from traditional SaaS, and getting this wrong early can quietly kill your margins.
Input vs. Output Tokens
Input tokens are cheap. Output tokens are expensive. A model generating a 2,000-word report costs roughly 4x more than one summarizing a 2,000-word document into five bullets. Your product design should account for this.
The Caching Opportunity
Most major providers now offer prompt caching. If your system prompt is long and consistent across requests, caching can cut costs by 60–80%. This single optimization is often worth more than a week of architecture work.