Cloudflare Rebuilds Containers for Agent Sandboxes with 6x Faster Startup and Runtime Image Selection

Cloudflare has redesigned Cloudflare Containers to optimize for AI agent workloads, introducing a new durable_object scheduling policy that shifts control from deployment-time configuration to application code. This change enables developers to select container images and instance types at runtime, eliminating the need for separate applications for each environment combination.

Performance Improvements

The redesign significantly accelerates container startup times. Independent benchmarks using the ComputeSDK show a 6.2x improvement in median time-to-interaction (TTI), dropping from 4.049 seconds to 648ms. The 95th percentile improved by 6.4x (from 5.839s to 910ms), and the 99th percentile by 5.9x (from 6.717s to 1129ms). Preliminary internal tests demonstrated the creation of 100,000 containers across six locations in 5.387 seconds using a single account.

Architecture and Key Features

• Runtime Configuration: Developers can now pass image and instance type arguments directly in code, accessible via this.ctx.container.images.<name>. This supports dynamic rollout strategies like canary deployments within Durable Object logic.
• Fast Startup: The system prioritizes scheduling on machines already hosting the Durable Object and reuses prepared VMs and network settings, avoiding full VM boots.
• File System Snapshots (Public Beta): Immutable snapshots allow multiple containers to start from the same baseline environment, facilitating session persistence and efficient evaluation or reinforcement learning workflows.
• System Image: A pre-deployed cloudflare/debian-trixie image (Debian Trixie Slim + Node.js 24.20.0 LTS) is available for immediate use without Dockerfile builds.

Migration and Availability

The new durable_object scheduling policy is available in public beta for all users. The legacy Container class and Sandbox class will be supported until December 31, 2026, but will not receive updates. Developers are encouraged to migrate to the ctx.container native API. Key migration steps include changing extends Container to extends DurableObject and utilizing this.ctx.container for direct calls. The Sandbox SDK 1.0 is now a utility set for use within Durable Objects, while @cloudflare/computer combines Dynamic Workers and Containers for synchronized file systems.