Fly Sprites vs Blaxel pricing, standby and limits

Which is better, Fly Sprites or Blaxel?

It depends on how fast the sandbox must come back and how many you run. Agents that idle between model calls cost least on Runtime: $0.64 for 1,000 one-minute runs, against $2.40 on Sprites and $3.45 on Blaxel. A paused sandbox keeps memory and processes while you have credit. Pick Fly Sprites for a 100 GB disk that costs little while it sleeps and takes filesystem checkpoints in about a second. Pick Blaxel to resume in milliseconds, or for fleets of more than 100,000 sandboxes running concurrently.

At a glance

What survives when a sandbox goes idle?

On Blaxel, everything inside the VM. A sandbox goes to standby about 15 seconds after its connections close. Open WebSocket and TCP connections time out after 15 idle minutes. Blaxel snapshots the whole state, including the filesystem and running processes. Blaxel says a reconnect resumes it in under 25 ms. Connections the sandbox held open to a database or an API do not survive. Blaxel keeps the writable filesystem in memory, which uses about half of the sandbox's memory.

On Sprites, the disk always, memory for a while. A Sprite pauses about 30 seconds after activity stops. In a warm pause, its memory is frozen. It resumes in 100 to 500 ms, and its processes carry on. Left longer, it goes cold. Memory is dropped, the next wake takes 1 to 2 seconds, and processes start fresh. Fly does not say when a warm pause turns cold. The 100 GB disk is kept, and storage costs little while asleep.

On Runtime, files, memory and processes, for as long as you choose. A paused sandbox is kept while you have credit on a paid account, at $0.08 per GB-month. Nothing drops its memory on a schedule you did not set.

Cost for the same job

1,000 runs of a 2 vCPU, 4 GiB sandbox (4 GB on both other providers). Each run lasts 60 seconds and keeps the CPU busy for 20 CPU-seconds: an agent that mostly waits for a model. The Sprite is assumed to use all 4 GB for the whole minute.

At 100,000 runs per month, that is $240.14 on Sprites, $345.00 on Blaxel and $63.89 on Runtime. With both CPUs busy for the whole minute, it is $1.33 on Runtime against $3.47 on Sprites and $3.45 on Blaxel, so Runtime is cheaper however busy the sandbox is. Busy work costs Sprites more because its CPU is metered. Blaxel's price does not change with the CPU. The Blaxel figure includes the 15 seconds or so each sandbox stays billed before standby. The Sprites figure includes the 30 seconds or so that a Sprite stays awake and billed after its run. Storage, network, plan fees and free credits are left out.

Which one to pick

• Pick Fly Sprites for a persistent computer an agent keeps coming back to, with a 100 GB disk that costs little while it sleeps and filesystem checkpoints that take about a second.
• Pick Blaxel if the sandbox must come back in milliseconds with its processes running, or for very large fleets: its top tier runs over 100,000 sandboxes concurrently.
• Pick Runtime for the lowest cost of the three while running, a pause that keeps memory while you have credit, and forks of a running sandbox.

Switch from either one

All three pause on their own. A Runtime sandbox pauses after 300 seconds with nothing happening in it, or after the idlePauseSeconds you set. Any request wakes it. To keep one sandbox per user or task, found by name:

TypeScriptimport { Sandbox } from "withruntime";const dev = await Sandbox.getOrCreate("agent-42", { idlePauseSeconds: 60 });await dev.exec("git pull || true"); // wakes it first if it was paused

From Sprites, client.createSprite(name) becomes Sandbox.create(). To reach a sandbox by name again, use Sandbox.getOrCreate(name). sprite.execFile(cmd, args) becomes exec([cmd, ...args]). Blaxel code runs unchanged after you import SandboxInstance from withruntime/blaxel (Python withruntime.blaxel). Its standby maps to automatic wake, which is on by default. Or give your coding agent the one instruction in migration. It switches the project on a branch, tests it on the free usage, and reports the monthly saving. npx withruntime compare --from fly (or --from blaxel) prices what you ran at the old provider's rates. Credit you add within 30 days of signing up is matched, up to $1,000 in total. The full side-by-sides are Runtime vs Fly.io and Runtime vs Blaxel.

Sources

Fly.io prices checked 25 October 2026.

Sprites rates checked 25 October 2026, and the Sprites and Sprites lifecycle pages read 26 October 2026. Blaxel rates checked 25 October 2026, with its pricing page and sandbox documentation.

• Fly.io pricing, Sprites, Sprites lifecycle
• Blaxel pricing, Blaxel sandboxes
• Runtime pricing and how to pause and resume a sandbox

Facts on this page were checked on 26 October 2026.