Building with Bun and Cosmic: The Fastest JavaScript Stack in 2026

Tony Spiro Posted on May 30 • Originally published at cosmicjs.com           Building with Bun and Cosmic: The Fastest JavaScript Stack in 2026 # javascript # bunjs # webdev # api 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. That acquisition signals something: the fastest JavaScript runtime is also where serious AI tooling is heading. Bun is built on JavaScriptCore (the engine that powers Safari) and written in Zig. It ships as a single binary that includes a runtime, package manager, bundler, and test runner. In practice this means: Install speed: Bun installs packages up to 25x faster than npm. With v1.3.14's global store, warm reinstalls are 7x faster again. Startup time: Cold start times are significantly lower than Node.js, particularly for TypeScript projects where Bun transpiles natively without a separate build step. Async/await performance: Bun v1.3.7 shipped 35% faster async/await. v1.3.6 brought 15% faster async/await on top of that. Built-in tooling: No tsconfig.json gymnastics, no separate transpiler, no test framework to