Originally published on the Cosmic blog . Bun v1.3 is the fastest JavaScript runtime you can use right now. Cosmic's REST API returns content in under 100ms. Put them together and you get a full-stack setup that's faster at every layer: cold starts, package installation, HTTP requests, and content delivery. This is a practical tutorial. You'll set up a Bun project, pull content from Cosmic using the JavaScript SDK, and see why this combination is the right default for JavaScript developers building content-heavy apps in 2026. Bun is also actively rewriting core internals in Rust, doubling down on raw performance and memory safety. This isn't just an optimization story: it signals a long-term commitment to speed as a first-class priority. Why Bun in 2026 Bun started as a fast alternative to Node.js, but in December 2025 it was acquired by Anthropic, which is now betting on it as the runtime infrastructure powering Claude Code and the Claude Agent SDK.…