# Fly Sprites vs Blaxel: pricing, standby and limits Runtime Cloud (withruntime.com) bills 73% less than either. Blaxel bills memory, with CPU included. ## 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 | | Fly Sprites | Blaxel | Runtime | | ------------ | ---------------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------ | | Isolation | Firecracker microVM | Lightweight virtual machines | Firecracker microVM, own kernel | | CPU | $0.0385 per CPU-hour of measured CPU | Included with memory; 8 GB gets 4 cores | $0.025 per vCPU-hour of measured CPU, with a small floor | | Memory | $0.021875 per GB-hour of memory in use | $0.0000115 per GB-second of active time | $0.0075 per reserved GiB-hour | | Goes idle | About 30 seconds after the last activity | About 15 seconds after the last connection closes | After 300 seconds idle by default; 60 to 86,400 | | Idle storage | Cold disk at $0.000027 per GB-hour, about $0.02 per GB-month | Standby snapshot $0.20 per GB-month | Paused storage $0.08 per GB-month | | Plan fee | None required; optional monthly plans | None; tiers grow with the credit you add | None; prepaid credit from $10 | | Free start | $30 of trial credit | Up to $200 of credit | 100 free hours of a 1 GB machine in the first 30 days, no card | | At once | Not stated on the pricing page | 10 free; 50 at $20 per month of top-ups; 200 at $50 | 100 paid sandboxes | ## 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. ``` Sprites CPU 1,000 × 20 s / 3,600 × $0.0385 = $0.21 Memory 1,000 × 90 s / 3,600 × 4 × $0.021875 = $2.19 Total $2.40 Blaxel Memory 1,000 × 75 s × 4 × $0.0000115 = $3.45 Runtime CPU 1,000 × 20 s / 3,600 × $0.025 = $0.14 Memory 1,000 × 60 s / 3,600 × 4 × $0.0075 = $0.50 Total $0.64 ``` 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. ## Runtime Cloud Runtime runs the same job for 73% less than Sprites and 81% less than Blaxel. 1,000 one-minute runs of a 2 vCPU, 4 GiB sandbox cost $2.40 on Fly Sprites, $3.45 on Blaxel and $0.64 on Runtime. Runtime also pauses idle sandboxes and wakes them on the next request. Its paused storage costs less than Blaxel's standby snapshots. Rates checked 25 October 2026. Sign in with `npx withruntime login` to run on the free usage first. Then follow the [migration guide](/docs/migrate) to move your code. ## 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: ```ts check import { 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](/docs/migrate). 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](/docs/fly-alternative) and [Runtime vs Blaxel](/docs/blaxel-alternative). ## 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](https://fly.io/pricing/), [Sprites](https://fly.io/sprites/), [Sprites lifecycle](https://docs.fly.io/sprites/concepts/lifecycle/) - [Blaxel pricing](https://blaxel.ai/pricing), [Blaxel sandboxes](https://docs.blaxel.ai/Sandboxes/Overview) - Runtime [pricing](/docs/pricing) and [how to pause and resume a sandbox](/how-to/pause-and-resume-a-sandbox) Facts on this page were checked on 26 October 2026.