Stop Guessing: How I Pick AI API Architecture at Every Scale
Stop Guessing: How I Pick AI API Architecture at Every Scale I've been on both sides of this. Two years ago I was the lone backend engineer at a Series A startup, duct-taping API calls together at 2 AM because the founders wanted a chatbot demo by morning. Last quarter I sat in a procurement meeting at a Fortune 500 where we spent six weeks evaluating three vendors for a single inference workload. Same job title on LinkedIn, wildly different problems. Most AI API guides I've read treat both scenarios like they're the same conversation. They're not. The startup CTO optimizing for burn rate and the enterprise architect worrying about a 99.9% uptime SLA are solving fundamentally different equations. After enough of these conversations, I've developed a framework I'd like to share — and yes, I'll talk about Global API because it's what I actually use, but I'll also explain the reasoning behind each choice so you can adapt it to your own stack. What I Look at First: The p99 Question Before I look at price, I look at the latency distribution. Specifically, the p99. Mean latency tells you almost nothing useful. If your median response is 200ms but your p99 is 4 seconds, your users will see janky behavior on the long tail and you won't know why until production is on fire. For startups in the MVP phase, you can usually get away with best-effort routing. A p99 of 2-3 seconds is fine if you're building an async summarization feature. But the moment you put AI in the synchronous request path — like a customer-facing chatbot or a real-time code suggestion — p99 starts to bite. I learned this the hard way when our startup's "AI assistant" feature had users complaining about slowness that I couldn't reproduce locally. The culprit? Provider cold starts hitting our 1% of users who happened to get routed to a freshly spun-up instance. For enterprises, p99 isn't a nice-to-have, it's a contractual obligation. Most B2B SLAs I've negotiated pin uptime at 99.9% and require reporting on m