I Cut Our Image Captioning Costs 60% — Here's the Backend Story
Check this out: i Cut Our Image Captioning Costs 60% — Here's the Backend Story Look, I'll be honest. Six months ago I didn't think twice about image captioning. We were a small team, traffic was low, and we just threw everything at GPT-4o because it was the path of least resistance. Then our infra bill came in, my manager did that thing where he just stares at the dashboard, and suddenly I was a "cost optimization" guy. fwiw, that was not in my job description. This is the story of how I went from "we just use GPT-4o for everything" to a multi-model setup that cut our spend by more than half, with quality that — imho — is actually better than what we had before. No, this is not a sponsored post. Yes, I am going to mention Global API at the end because they made my life easier. More on that in a bit. Why Image Captioning Was Even on My Radar Our product has a lot of user-uploaded images. Think: product photos, profile pictures, the usual suspects. For each one we need a short, accessible caption that we use for SEO, alt text, and a downstream tagging pipeline. The downstream pipeline, btw, is the part that actually makes us money. Garbage captions in, garbage tags out. We were calling gpt-4o for everything. Every image. No caching. No batching. No thought. Each call cost us $2.50 per million input tokens and $10.00 per million output tokens. You don't have to be a math PhD to know that scales badly. I was not a math PhD. I am still not a math PhD. But I can do division. When I started pulling the numbers, the situation was grim. We were processing roughly 8 million images a month, and each one was generating more tokens than it needed to. I found one image in the logs that had produced a 4,000-token caption. The image was a screenshot of an error message. The caption was longer than the error. The Wake-Up Call: Actually Reading the Catalog One Saturday morning, coffee in hand, I decided to actually look at what was on offer. I'd been ignoring the multi-model world b