Project Think: building the next generation of AI agents on Cloudflare (opens in new tab)
Project Think is Cloudflare’s next-generation Agents SDK for building persistent, scalable AI agents. It combines durable execution, sub-agents, persistent sessions, sandboxed code execution, and runtime-created extensions, while allowing developers to use individual primitives or an integrated Think base class. Its central argument is that agents should run as durable, one-to-one infrastructure rather than ephemeral processes on laptops or permanently running servers. ## Why Agents Need a New Foundation - Coding agents increasingly act as general-purpose assistants by reading context, writing and executing code, observing results, and iterating. - Existing agents are limited by: - Dependence on a laptop or costly VPS - Fixed costs while idle - Manual installation, updates, identity, and secret management - Unlike traditional applications, agents are typically one-to-one: each user, task, or conversation may require a distinct agent. - Supporting millions of concurrent agents with always-on containers would be economically impractical. ## Project Think’s Core Primitives Project Think introduces: - Durable execution through fibers, including checkpointing, crash recovery, and automatic keepalive - Isolated sub-agents with independent SQLite databases and typed RPC - Persistent, searchable sessions with message trees, branching, and compaction - Sandboxed code execution using Dynamic Workers, codemode, and runtime npm resolution - An execution ladder spanning workspaces, isolates, npm packages, browsers, and sandboxes - Self-authored extensions that let agents create tools dynamically ## Long-Running Agents with Durable Objects - Each agent is implemented as a Durable Object with: - A stable identity - Persistent SQLite-backed state - Message-based wake-up - Automatic hibernation when idle - Agents can resume after HTTP requests, WebSocket messages, alarms, or inbound email. - Hibernated agents consume no compute, allowing many more agents than an always-on VM or container model. - Durable Objects provide automatic routing, recovery, and per-agent state without separately managed load balancers, databases, or process supervisors. - For example, 10,000 agents active only 1% of the time require capacity for roughly 100 active agents rather than 10,000 continuously running instances. ## Durable Execution with Fibers - Long LLM calls and multi-step workflows can be interrupted by deployments, restarts, or resource limits. - `runFiber()` makes a function invocation durable by: - Registering it in SQLite before execution - Allowing progress to be checkpointed with `stash()` - Recovering interrupted work through `onFiberRecovered` - Agents can save intermediate findings, resume from the latest checkpoint, and broadcast progress to clients. - The SDK automatically keeps the agent alive while a fiber runs. - `keepAlive()` and `keepAliveWhile()` support active work lasting minutes or longer, such as CI pipelines, design reviews, and video generation. Project Think’s recommendation is to treat agents as persistent, addressable infrastructure: use the low-level primitives for customization, or adopt the Think base class for a faster, integrated starting point.