Intel / blog

Cloudflare Containers, rebuilt to scale agent sandboxes

Source: blog.cloudflare.com
Date: Published Sep 30, 2026

Context

Cloudflare's revised Containers let an application choose an 's Linux workspace when a task arrives. Previously, the image and computing resources were fixed by the deployed application. A new scheduling policy lets the application's code select both at startup, so different tasks can receive different environments through the same controller. The architecture update explains the change.

Filesystem snapshots, in public beta, address a separate delay: rebuilding the workspace. They preserve files such as a repository, installed dependencies and edits, allowing a later container to resume from that saved state. A Durable Object, the persistent controller attached to each container, retains the workspace's identity and manages its lifecycle. Together these capabilities let applications stop Linux compute between sessions while retaining files needed for later work. Snapshot and controller details.

Key takeaways · AI-distilled

Because each picks its image in code at start time, rollouts need no platform config: Cloudflare suggests canarying a toolchain on 5% of new sandboxes by hashing the Durable Object ID, pinning active projects to their image, and rolling back by changing future starts.
On ComputeSDK's Burst TTI of 100 concurrent sandboxes, median startup fell from 4.049s to 648ms and p99 from 6.717s to 1.129s. Cloudflare credits placement near the Durable Object, hosts with the image cached, and restoring prepared VMs instead of booting fresh.
Snapshots are immutable and reusable, so one snapshot can seed many isolated sandboxes from the same baseline. Cloudflare pitches this for comparing prompts, models or agent versions without environment drift, and for RL coordinators that fork and grade attempts.
Cloudflare's migration guidance warns that a snapshot restores only on the image it was taken from, so an image deploy can lock users out of workspaces whose files live only in snapshots. It says to keep file-level backups as the source of truth.
New features are available only through ctx.container. The Container class and legacy Sandbox class are maintained through December 31, 2026 and then stop getting updates; migrating usually means changing extends Container to extends DurableObject.

Terms in this piece · Glossary

AI agent — An AI system that doesn't just answer once but works toward a goal in a loop — taking actions, reading the results, and deciding what to do next.
sandbox — An isolated environment where AI-generated code or agent actions run without being able to touch anything real.
benchmark — A standard public test set for comparing AI models — the shared scoreboards behind every "model X beats model Y" claim.
eval — A repeatable test for AI quality — a set of tasks plus scoring — used the way software teams use test suites, because model output is too variable to judge by eyeballing.

Read the source blog.cloudflare.com