How I Cut a Client's AI API Bill from Rs 85,000 to Rs 12,000 a Month

₹85,000 per month. That was the AI API bill sitting in my client's inbox when they called me in a mild panic last quarter. They run a mid-sized e-commerce operation in Pune — about 4,000 orders a day — and had integrated AI into customer support, product descriptions, and internal reporting. The AI was working beautifully. The invoice was not. Three weeks later, their monthly bill was ₹12,400. Same tasks. Same quality. No corners cut. Here's exactly what changed. The real problem: every task was using the most expensive model When I audited their setup, the issue was obvious within five minutes. Every single API call — whether it was classifying a customer complaint into one of 8 categories or generating a 2,000-word product description — was hitting the same premium model. It's the most common mistake I see with businesses adopting AI: they pick one model during the proof-of-concept phase and never revisit that decision as they scale. You wouldn't hire a senior chartered accountant to do data entry. But that's essentially what was happening — a top-tier reasoning model answering "Is this complaint about shipping or billing?" Fix 1: Model routing — the single biggest cost lever Model routing means sending each task to the cheapest model that can handle it at acceptable quality. I categorised their ~47 distinct API call types into three tiers. 68% of calls moved to the lightweight tier, 20% to mid-tier, only 12% stayed on premium. That single change dropped the bill from ₹85K to roughly ₹38K — no quality loss, verified with two weeks of A/B testing on customer satisfaction scores before switching fully. Fix 2: Prompt caching — stop paying for the same context twice Their support bot sent the same 1,200-token system prompt with every call — policies, tone, catalogue context, all identical across thousands of daily calls. Caching processes it once and references it cheaply on subsequent calls within the window. At ~6,000 support interactions a day, this alone saved ₹8,