Prompt Caching in 2026: Anthropic vs OpenAI vs Gemini for Production Apps

I opened the billing dashboard for one of my AI features a few months ago and felt my stomach drop. The feature was working beautifully. Users loved it. Traffic was climbing. And the monthly spend had quietly crossed a line that made me open a second tab to check the math twice. I had been telling myself caching was on the "optimize later" list for about three months. That morning it moved to the top. What I learned over the next two weeks is that prompt caching is not an optimization. It is the difference between a production AI feature that pencils out and one that eats your margin alive.