Cloudflare Project Think Durable Agent Runtime 2026

Date: 2026-05-13
Track: sandbox-poc
Slug: cloudflare-project-think-durable-agent-runtime-2026
Status: Source-based PoC (no live API keys available; package install verified)

Environment

OS: macOS Darwin 24.6.0 (Apple Silicon)
Node.js: v22 (Cloudflare Workers requirement)
npm: v10+
Cloudflare Workers account: not available in sandbox; package install only

What Was Verified

Package Installability

Checked package registry for @cloudflare/think:

npm show @cloudflare/think version
# Result: 0.0.1-experimental.3 (as of 2026-05-13)

Install command as documented:

npm install @cloudflare/think agents ai @cloudflare/shell zod workers-ai-provider

All packages resolved successfully to the npm registry. No build errors on install dry-run.

GitHub Repository Inspection

Repository: github.com/cloudflare/agents — 30+ self-contained demo scripts in /examples/. Key files confirmed:

docs/think/index.md — Think base class overview
packages/think/src/index.ts — exports Think, Session, runFiber
packages/shell/src/index.ts — exports Workspace (SQLite + R2 filesystem)

SDK Surface Confirmed

From official docs (developers.cloudflare.com/agents/api-reference/think/):

import { Think } from "@cloudflare/think";
import { createWorkersAI } from "workers-ai-provider";

export class MyAgent extends Think<Env, unknown> {
  getModel() {
    const ai = createWorkersAI({ binding: this.env.AI });
    return ai("@cf/meta/llama-3.3-70b-instruct");
  }
}

Execution Ladder Tiers — Confirmed from Docs

Tier	Name	Package / API	Capability
0	Workspace	`@cloudflare/shell`	Durable filesystem, SQLite + R2
1	Dynamic Worker	`@cloudflare/codemode`	Sandboxed V8 isolate, no network
2	npm	`@cloudflare/worker-bundler`	Fetch npm pkgs, esbuild, load in DW
3	Browser	Cloudflare Browser Run	Navigation, click, extract
4	Sandbox	`cloudflare/sandbox-sdk`	Full Linux env, git, npm test, cargo

Fiber Primitive — Conceptual Reproduction

Source: blog.cloudflare.com/project-think/, noise.getoto.net/2026/04/15/...

import { runFiber } from "@cloudflare/think";

// Fibers checkpoint at ctx.stash() calls.
// If the worker restarts, execution resumes from the last stash() point.
async function longTask(ctx) {
  const step1 = await doExpensiveWork();
  await ctx.stash({ step1 });   // checkpoint saved to SQLite

  const step2 = await callExternalAPI(step1);
  await ctx.stash({ step1, step2 });

  return finalize(step1, step2);
}

export class MyAgent extends Think<Env, unknown> {
  async onTask(task: string) {
    return runFiber(this.ctx, () => longTask(this.ctx));
  }
}

This pattern is the key architectural difference from standard Cloudflare Workflows: fibers are co-located with the Durable Object and use its SQLite for checkpointing, so there is no separate Workflow state machine.

Sub-Agents (Facets) — API Surface Confirmed

From developers.cloudflare.com/agents/api-reference/sub-agents/:

// Parent spawns a child with typed RPC
const facet = await this.spawnFacet("data-processor", DataProcessorAgent);
const result = await facet.processChunk(data);

Each facet (child Durable Object) has:

Isolated SQLite storage
Own execution context
Typed RPC stub returned to parent
Colocated on the same machine as parent

Session API — Confirmed Structure

From developers.cloudflare.com/agents/api-reference/sessions/:

Messages stored as relational tree (parent_id FK)
Fork: create branch from any node without modifying main path
Compaction: non-destructive summarization as context overlay
Full-text search: FTS5 index over all messages

What Was NOT Tested

End-to-end agent deployment (requires Cloudflare Workers account + paid plan)
Actual fiber crash recovery in production (no production env)
Browser Run and Sandbox tiers (require Workers Paid plan + specific bindings)
Real LLM inference via @cf/meta/llama-3.3-70b-instruct

Limitations

Project Think is experimental preview as of 2026-05. API surface is stable but may evolve.
Dynamic Workers require Workers Paid plan.
Cloudflare Sandbox tier (Tier 4) requires additional sandbox binding configuration.
No public benchmark data comparing fiber checkpointing overhead vs. re-execution.