Cloudflare previews Project Think for durable, long-running agents

Cloudflare previewed Project Think on April 15 as a new set of primitives for its Agents SDK. The announcement covers durable execution, isolated subagents, persistent sessions, sandboxed code execution, and an opinionated Think base class that assembles those parts for long-running agent applications.

Agent state moves into platform infrastructure

Project Think builds on Durable Objects, giving each agent an addressable instance and SQLite-backed state. Its fiber abstraction records a long-running invocation before execution, supports checkpoints, and exposes a recovery hook after a restart. Persistent sessions store messages as a tree so an application can fork or compact a conversation without discarding its history.

Subagents receive separate state and communicate with a parent through typed RPC. Cloudflare also describes an execution ladder that can place work in environments with different capabilities, from a workspace or isolate to browser and sandbox contexts. The release is explicitly a preview, and Cloudflare says its APIs may evolve.

Recovery semantics need application tests

Durable infrastructure cannot decide whether an external action is safe to repeat. A team evaluating fibers should interrupt a workflow between checkpointing and a tool call, then verify what recovery does. Payments, messages, and deployments need idempotency keys or an application record that distinguishes requested, completed, and uncertain outcomes.

Subagent boundaries also deserve a permissions review. Separate SQLite state improves isolation of conversational context, but each child should receive only the tools and secrets required for its task.

The preview gives developers concrete building blocks for agents that outlive a browser tab or laptop process. Adoption should still pin package versions, record which preview APIs the application depends on, and include migration work in the operational plan.