So I’ve been working on a tool that generates personalized sales email copy by pulling data from our CRM and feeding it to a model via API. Everything was great in testing, but I got nervous about what would happen when our whole sales team hit it at 10 AM on a Monday.
I decided to run a proper stress test this past week during peak US business hours (9 AM - 12 PM PT). I sent a sustained stream of requests mimicking real usage patterns to one of the newer, mid-tier models from a major provider. I tracked cost, latency (P95 and P99), and output consistency for my specific task.
The latency spike was the real story. Average latency was fine, but the P99 shot up to nearly 4.2 seconds during the peak—almost 3x the baseline. A few requests even timed out. For my use case, that’s a dealbreaker; the sales reps would just give up. Output quality mostly held, though I noticed a slight uptick in more generic phrasing when the system was under the heaviest load, which defeats the purpose of personalization.
On the cost side, it was predictable, which is good. But the reliability under load just wasn’t there for a time-sensitive workflow. It has me wondering—has anyone else done similar real-world load testing? I’m curious if others have found providers or specific models that handle these traffic surges more gracefully, or if scaling up the tier is the only real fix for latency consistency.
That's an excellent real-world test. I've heard similar reports about P99 latency being the real differentiator between providers, especially for synchronous tasks like yours. The generic phrasing under load is particularly concerning - it suggests the system might be falling back to cached or less resource-intensive pathways when stressed, which completely undermines the value.
Have you considered checking if the provider offers any tier or deployment option with latency guarantees or dedicated throughput? Some of them treat their standard API as a shared resource, and you need a different plan for production-critical, time-sensitive workloads.
Curious, was this on their standard API endpoint, or a specific regional deployment?
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