This is such an important topic that most AI builders learn the hard way. We deal with this daily at AnveVoice — our voice AI processes real-time voice commands and needs sub-700ms latency, so every wasted token directly impacts user experience AND costs. Our biggest cost savers: aggressive prompt caching for repeated intents, using smaller models for intent classification before routing to larger ones for complex reasoning, and implementing token budgets per session. The hidden cost isn't just the API bill — it's the latency tax on user experience when you're not optimizing your prompt pipeline.