# 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](/docs/storage#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](/glossary/egress-fees).

## 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](/docs/storage) that
outlives sandboxes, and snapshots copied off their server
([snapshots survive their server](/docs/storage#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](/how-to/mount-an-s3-bucket)
- [What are egress fees?](/glossary/egress-fees)
- [What is a sandbox snapshot?](/glossary/sandbox-snapshot)
- [What is workload identity?](/glossary/workload-identity)

## Sources

Checked 27 September 2026.

- [What is Amazon S3?, AWS](https://docs.aws.amazon.com/AmazonS3/latest/userguide/Welcome.html)
- [Cloudflare R2 pricing](https://developers.cloudflare.com/r2/pricing/)