FastAPI vs Django vs Flask: What I Actually Use After Testing All Three in 2026

Three weeks ago I needed to pick a framework for a client project — a B2B analytics API with roughly 200 daily active users, a team of three backend engineers including me, and a hard requirement to expose several LLM inference endpoints. I've shipped production apps on all three of these frameworks at different points in my career, but I hadn't done a real side-by-side comparison in over two years. So I spent two weeks spinning up the same feature set in each one and taking notes. Here's what I found. FastAPI Has Quietly Become the Default for New Python APIs When FastAPI first blew up, I was skeptical. Another micro-framework? Python doesn't exactly have a shortage of those. But FastAPI 0.115 (released late 2025) has matured in ways that make it genuinely hard to argue against for API-first projects. The Pydantic v2 integration is the main thing. With Pydantic v2 as the validation layer, you're getting roughly 5-10x faster serialization compared to v1 — and FastAPI leans into this ha