Cloudflare just turned its Agents SDK into an open runtime. Flue is the first framework on it.

Cloudflare open-sourced the Agents SDK as a base layer any harness can build on.

Flue, from the Astro team, shipped 1.0 Beta on top of it.

The real story isn't the framework. It's the three-layer stack that just got formalized.

Framework (Flue) → Harness (Pi/Project Think) → Runtime (Agents SDK).

Your agent doesn't need 50 tools. It needs one tool that executes code.

That's the pattern. The model writes a TypeScript function, the harness runs it in a Dynamic Worker isolate. 10ms startup. $0.002 per load. Each snippet gets a fresh isolate, executes, and is discarded.

This eliminates tool surface bloat — the problem where models degrade as tool definitions pile up and context windows fill.

Under the hood, Flue agents deploy as Durable Objects. Each agent gets isolated storage, compute, and a durable filesystem backed by SQLite via @cloudflare/shell.

Crash recovery is handled by Fibers: runFiber() checkpoints to SQLite before work starts, stash() advances the checkpoint, onFiberRecovered() tells a fresh instance exactly where to resume.

No spinner that never resolves. No lost context. No wasted tokens replaying an entire turn.

If you're building agents today:

Audit your tool surface. Count the tools your model selects from. If it's over 15, you're losing selection accuracy.

Test the code-execution pattern. One tool that runs generated code beats a curated tool catalog every time.

If you're deploying on Cloudflare, Flue targets Agents SDK natively. Every Durable Object gets fibers, codemode, and the virtual filesystem out of the box.

If you're not on Cloudflare, the pattern still applies. Durable execution + code-mode is the architecture. The platform is the detail.

Source: https://blog.cloudflare.com/agents-platform-flue-sdk/
Verified: Cloudflare Blog (June 17 2026), GitHub withastro/flue (5320 stars), npm @flue/runtime