What is object storage?
Object storage keeps data as whole objects in buckets, each addressed by a key over HTTP, not as files in folders or disk blocks.
A Runtime sandbox mounts your bucket in Amazon S3, Cloudflare R2 or Google Cloud Storage as a folder without ever holding the bucket's key. You store the key once as a secret, and the host signs the sandbox's requests on the way out, so code in the sandbox reads and writes the files and cannot copy the credential (mount your own bucket).
How it is organised
Amazon's S3 guide gives the model in three nouns. An object "is a file and
any metadata that describes the file". A bucket "is a container for
objects". A key "is the unique identifier for an object within a bucket".
There are no real directories: photos/puppy.jpg is one key that happens to
contain a slash.
Object, block and file storage
| Kind | Addressed by | Changed by | Typical use |
|---|---|---|---|
| Object | Bucket and key, HTTP | Replacing the whole object | Datasets, backups, media, build outputs |
| Block | A disk's block numbers | Writing any block | A machine's root disk, databases |
| File | A path in a tree | Writing part of a file | Shared folders, home directories |
Object stores trade in-place edits for scale and price: S3 promises strong read-after-write consistency, and Cloudflare R2 stores data for $0.015 per GB-month with no charge for egress.
Object storage and sandboxes
An agent's input data usually already lives in a bucket. Mounting it saves the download on every run, and keeping the key on the host means a prompt injection in that data cannot send the credential anywhere. Runtime keeps its own state on disks instead: a sandbox's files, a volume that outlives sandboxes, and snapshots copied off their server (snapshots survive their server). Runtime does not sell an object store of its own today; it mounts yours.
Related
- How to mount an S3 bucket in a sandbox
- What are egress fees?
- What is a sandbox snapshot?
- What is workload identity?
Sources
Checked 27 September 2026.