Starlette 1.0 Released After 8 Years — But LLMs Are Trained on Pre-1.0 Code

Simon Willison's Blog·medium signal

Starlette 1.0.0 shipped March 22, 2026 — 8 years after creation, now at 325M downloads/month (6x growth from 57M/month a year ago), the foundation of FastAPI. Simon Willison identified a practical problem: LLMs are trained on pre-1.0 Starlette code and will generate incompatible patterns, solving it by building a custom Claude skill document from the 1.0 docs so Claude generates correct 1.0 code going forward. This is a replicable pattern for any post-training framework version upgrade.