Fly.io Sprites
Fly.io Sprites are persistent, stateful Linux virtual machines built as sandboxes for AI agents. Each Sprite is a hardware-isolated Firecracker microVM with a full Linux filesystem that survives across runs. Sprites scale to zero (hibernate when idle, wake on the next request) so agents can keep long-lived state and installed tools between sessions. They expose a REST and WebSocket API and are intended for executing untrusted or agent-generated code in isolation, with built-in features for checkpoints, file transfer, port forwarding, and outbound network policy.
| Pricing model | Usage-based hourly metering: CPU usage and actual memory, plus hot storage while awake and cold storage while retained |
|---|---|
| Pricing The headline compute price as the provider states it. Sorting ranks prices stated per vCPU over time, converted to hourly. Other pricing models sort after, unranked. | $0.0385 per CPU-hour; $0.021875 per GB-hour of memory |
| Free while idle Whether a stopped, paused, or sleeping sandbox costs nothing. | ✓ |
| Elastic Resources flex with what the sandbox actually uses, and the bill follows: yes when the provider bills on active or observed use, no when capacity is reserved or allocated and billed while it runs. | ✕ |
| Memory snapshots Whether RAM state survives a pause and resume, not just disk. | ✓ |
| Wake on request Whether a stopped sandbox wakes automatically on inbound traffic. | ✓ |
| Start / resume Typical time from create or resume to running. Sorting ranks stated times, converted to seconds; claims with no figure sort after, unranked. | ~100-500 ms warm resume; ~1-2 s cold start |
| Max runtime The longest a sandbox may run. | No fixed limit |
| Isolation The isolation technology between sandboxes. | Firecracker microVM |
| GPUs Whether GPU instances are available for sandboxes. | ✕ |
| Docker Whether Docker containers can run inside the sandbox. | ✓ |
| SDKs | Go, JavaScript/TypeScript, Python, Elixir |
✓ yes · ✕ no · – no cited public fact.
Sprites intentionally drop OCI/Docker container images: every Sprite boots from a standard base image and software is installed directly on the filesystem. A paused Sprite suspends warm first, with the VM frozen in memory, and the next request resumes processes where they left off. If it stays idle it falls to cold on its own and drops in-memory state, so any process the agent needs to keep alive across a sleep must be registered as a Sprites 'Service' that auto-restarts on wake. An idle Sprite accrues no compute charges and hot storage stops billing while it sleeps, but cold storage bills until the data is deleted, at $0.02 per GB-month.
Sources
- https://community.fly.io/t/how-to-get-docker-running-on-sprites/27168
- https://github.com/superfly/sprites-go
- https://github.com/superfly/sprites-js
- https://github.com/superfly/sprites-py
- https://github.com/superfly/sprites-ex
- https://docs.sprites.dev/api/dev-latest/
- https://fly.io/
- https://community.fly.io/t/sprite-constantly-stays-warm-also-any-way-to-reboot/26926
- https://docs.sprites.dev/concepts/checkpoints
- https://docs.sprites.dev/concepts/lifecycle/
- https://fly.io/blog/design-and-implementation/
- https://fly.io/learn/fly-vs-modal/
- https://news.ycombinator.com/item?id=46634450
- https://docs.sprites.dev/
- https://docs.sprites.dev/working-with-sprites/
- https://docs.sprites.dev/keeping-sprites-running/
- https://community.fly.io/t/sprites-not-shutting-off/26793
- https://fly.io/pricing/
- https://fly.io/sprites/
- https://fly.io/sprites/release-notes/
Last verified 2026-10-06. Corrections land through the update log.