Which is better, Fly Sprites or Runloop?
It depends on whether you need a persistent computer or a platform for agent evaluation. For agents that mostly wait on a model, Runtime has the lowest bill: $0.64 for 1,000 one-minute runs, against $2.40 on Sprites and $5.33 on Runloop. Its pause also keeps processes running. Pick Fly Sprites for a 100 GB disk that costs little while asleep, and for filesystem checkpoints in about a second. Pick Runloop for SWE-Bench runs that Runloop runs for you, devboxes inside your own cloud account, and stated readiness for SOC 2, HIPAA and GDPR.
At a glance
| Fly Sprites | Runloop | Runtime | |
|---|---|---|---|
| Isolation | Firecracker microVM | microVM, with a container inside | Firecracker microVM, own kernel |
| CPU | $0.0385 per CPU-hour of measured CPU | $0.108 per CPU-hour while the devbox runs | $0.025 per vCPU-hour of measured CPU, with a small floor |
| Memory | $0.021875 per GB-hour of memory in use | $0.0252 per GB-hour | $0.0075 per reserved GiB-hour |
| Disk | 100 GB, billed on use: $0.000683 per GB-hour awake | $0.00034236 per GB-hour; MEDIUM comes with 8 GB |
Included while running |
| Sizes | Memory managed by Fly | X_SMALL (0.5 CPU, 1 GB) to XX_LARGE (8 CPUs, 32 GB) |
Up to 16 vCPUs and 64 GiB (paid), chosen separately |
| Plan fee | None required; optional monthly plans | Basic free; Pro $250 a month plus usage | None; prepaid credit from $10 |
| Free start | $30 of trial credit | $50 of credit, no card | 100 free hours of a 1 GB machine in the first 30 days, no card |
| Asleep | Disk kept; memory kept while warm, dropped when cold | Disk kept; processes restart; storage still charged | Files, memory and processes kept while you have credit |
What is kept when the sandbox sleeps?
A Sprite always keeps its disk, and keeps its memory for a while. It pauses by itself about 30 seconds after activity stops. A warm pause freezes memory. The Sprite resumes in 100 to 500 ms, with its processes still in progress. If it stays idle, it goes cold: memory is dropped, the next wake takes 1 to 2 seconds, and processes start fresh. Fly does not say how long the warm stage lasts. Open TCP connections do not survive either. A sleeping Sprite is not billed for compute, and its cold disk costs $0.000027 per GB-hour.
A Runloop devbox keeps its disk. Its lifecycle docs say suspend and resume preserve disk state, not memory. The devbox keeps its ID and SSH keys. Compute is billed only while the devbox is initializing, running, suspending or resuming. A suspended devbox still pays for storage until it is shut down.
A Runtime sandbox keeps everything. pause() saves its files, memory and running
processes while you have credit on a paid account, at $0.08 per GB a
month. The next request wakes it by itself, and it resumes where it stopped. See how to pause and resume a sandbox.
Cost for the same job
A thousand runs, one minute each, on 2 vCPU and 4 GiB. The code works for
20 CPU-seconds in each run and waits the rest of the time. The Sprite is
charged as if its full 4 GB were in use for all 60 seconds and the 30 or so it
stays awake after. On Runloop the size
is MEDIUM: 2 CPUs, 4 GB and an 8 GB disk.
- CPU
- 1,000 × 20 s / 3,600 × $0.0385
- $0.21
- Memory
- 1,000 × 90 s / 3,600 × 4 × $0.021875
- $2.19
- CPU
- 1,000 × 60 s / 3,600 × 2 × $0.108
- $3.60
- Memory
- 1,000 × 60 s / 3,600 × 4 × $0.0252
- $1.68
- Disk
- 1,000 × 60 s / 3,600 × 8 × $0.00034236
- $0.05
- CPU
- 1,000 × 20 s / 3,600 × $0.025
- $0.14
- Memory
- 1,000 × 60 s / 3,600 × 4 × $0.0075
- $0.50
For 100,000 runs a month, the cost is $240.14 on Sprites, $532.56 on Runloop and $63.89 on Runtime. When both CPUs are busy for the whole minute, the cost is $1.33 on Runtime, $3.47 on Sprites and $5.33 on Runloop. Between the two rivals, Sprites cost clearly less while the code waits, and still less when the code is busy, though the gap narrows because Runloop's price ignores CPU load. Plan fees, storage while asleep, network and free credit are excluded.
Which one to pick
- Fly Sprites: a 100 GB disk that costs little while asleep, and filesystem checkpoints in about a second.
- Runloop: evaluation on your own workload and RL rollouts, devboxes inside your own cloud account, and stated readiness for SOC 2, HIPAA and GDPR.
- Runtime: processes that keep running after a pause, measured CPU at $0.025 per vCPU-hour, and no plan fee. A benchmark harness built on it is in agent evals and SWE-bench.
Runtime Cloud
Runtime runs this job for 73% less than Sprites and 88% less than Runloop. Its pause is the only one of the three that keeps processes for as long as it lasts. 1,000 one-minute runs of a 2 vCPU, 4 GiB sandbox cost $2.40 on Fly Sprites, $5.33 on Runloop and $0.64 on Runtime. A cold Sprite and a suspended devbox both come back with their processes restarted. A paused Runtime sandbox comes back with its memory and processes as they were, for as long as you keep it paused. Rates checked 25 October 2026.
There is no plan fee. Start on the free usage with npx withruntime login, and move existing code with the migration guide.
Pausing and coming back
Both rivals approximate this pattern: pause a sandbox, reconnect later, even from a different process, and find its state as you left it.
Pythonfrom withruntime import Sandboxsbx = Sandbox.create(timeout_seconds=600)sbx.exec("echo state > /workspace/state.txt")sbx.pause() # memory, files and processes kept; compute billing stopsagain = Sandbox.connect(sbx.id)again.wake(timeout_seconds=1200)print(again.exec("cat /workspace/state.txt").stdout)again.stop()Sprites code ports directly: client.createSprite(name) is
Sandbox.create(), and sprite.execFile(cmd, args) is exec([cmd, ...args]).
npx withruntime compare --from fly or --from runloop reprices past usage.
Credit you add within 30 days of signing up is matched, up to $1,000 in total. For a port
with no manual steps, use the migration guide. A coding agent makes the change on a branch,
on the free usage. Full comparisons:
Runtime vs Fly.io,
Runtime vs Runloop.
Sources
Fly.io prices checked 25 October 2026.
Rates checked 25 October 2026. The Sprites, Sprites lifecycle and Runloop sizes and lifecycle pages were read 26 October 2026.
- Fly.io pricing, Sprites, Sprites lifecycle
- Runloop pricing, Devbox sizes, Devbox lifecycle, Runloop
- Runtime pricing
Facts on this page were checked on 26 October 2026.