2026-06-178 min read2026 is the year agent harnesses go to production. The software that controls the model’s access to the outside world — harnesses like Codex, Claude Code, OpenCode, Pi, and Project Think — has matured to the point where teams are deploying agents as real, load-bearing infrastructure, not just prototypes. But building agents that survive production is hard.We learned this firsthand building Project Think as our first-party agent harness. In working with our customers to run agents in production, we found a common set of distributed systems problems that every agent faces when running in the cloud. When an agent is interrupted, how can it automatically and gracefully resume from where it left off, without losing context or wasting tokens? How can agents run untrusted code securely? How can agents use the tools they were trained for?A harness can’t solve these problems on its own. They’re tied to state, storage and compute — which means they’re dependent on the platform the agent runs on. That’s why we’re taking our learnings from hardening Project Think for production and bringing them to the Cloudflare Agents SDK as a base layer. Durable execution, dynamic code execution, a durable filesystem and dynamic workflows, now available to any harness building on Agents SDK.At the same time, a new layer has emerged above the harness. Frameworks like Flue wrap a harness with the project structures, conventions, integrations and developer experience that make agents productive to build. To solve these scaling challenges, there’s a new, three-layer stack that is emerging for building production-grade AI. Here is how the pieces fit together, moving from the user-facing developer experience down to the underlying platform primitives: The framework (Flue) — the project structure, the conventions, the integrations, the CLI and the developer experience for building agents.The harness (Pi, Project Think) — the agentic loop that calls tools, reads results, manages context and keeps going until the task is done.The runtime/platform (the Cloudflare Agents SDK) — the compute, state, and storage primitives everything above depends onThe Agents SDK is that bottom layer: it makes primitives like durable execution available to any harness and any framework. Flue, our new open-source framework from the team behind Astro, is the first to build on it. Here’s how.