# Fly Sprites vs Northflank: pricing, isolation and limits Sprites bill measured CPU and memory in use; Northflank bills allocated vCPUs and memory at lower rates, so it costs less here. **Metering CPU is not enough on its own: Runtime, which meters CPU and charges little for memory, costs 81% less than Sprites and 42% less than Northflank for a waiting agent.** 1,000 one-minute runs of a 2 vCPU, 4 GiB sandbox cost $3.31 on Fly Sprites, $1.11 on Northflank and $0.64 on Runtime. Runtime's CPU rate is about a third of Sprites', and its memory rate is below both. Rates checked 23 September 2026. ## At a glance Northflank's isolation and regions are from its sandbox page, read 25 September 2026. | | Fly Sprites | Northflank | Runtime | | ------------- | ------------------------------------------------------ | ----------------------------------------------------- | --------------------------------------------------------- | | Isolation | Firecracker microVM | A microVM with Kata Containers, or gVisor | Firecracker microVM, own kernel | | CPU | $0.07 per CPU-hour of measured CPU | $0.01667 per allocated vCPU-hour | $0.025 per vCPU-hour of measured CPU, with a small floor | | Memory | $0.04375 per GB-hour of memory in use | $0.00833 per GB-hour | $0.0075 per reserved GiB-hour | | Idle | Pauses itself about 30 seconds after the last activity | Ephemeral by default; volumes and databases for state | Pause keeps files, memory and processes, 1 to 365 days | | Lifetime | Persistent; the disk survives every pause | No forced time limit, in Northflank's words | Leases extended as often as needed, or `persistent: true` | | Plan fee | None required; optional monthly plans | None published for compute | None; prepaid credit from $10 | | Free start | $30 of trial credit | 2 free services and 1 free database | 50 sandbox hours, no card | | Sandbox model | A Sprite, created by name | A service with a deployment plan | A sandbox, created in one call | ## Is paying only for the CPU you use always cheaper? No. What matters is the price of each meter, and memory is where these two part company. A Sprite's memory costs $0.04375 per GB-hour; Northflank's costs $0.00833, about a fifth. In the example below, a Sprite's 4 GB of memory alone costs $2.92 per 1,000 runs, where Northflank's whole bill, CPU and memory, is $1.11. Metering CPU helps Sprites only on the CPU line: $0.39 for 20 CPU-seconds a run against Northflank's $0.556 for two allocated vCPUs. With both CPUs busy the whole minute, Sprites' CPU line rises to $2.33 and Northflank's stays where it was. Runtime pairs a metered CPU at $0.025 a vCPU-hour with the lowest memory rate of the three, $0.0075 per GiB-hour. That makes it the cheapest while an agent waits. Northflank's allocated vCPU rate is lower still, so for work that keeps every CPU busy the whole time, Northflank costs less. ## Cost for the same job Priced for 1,000 runs of 60 seconds on 2 vCPU and 4 GiB (4 GB on each rival), with 20 CPU-seconds of computing per run. The Sprite is billed as though all 4 GB are in use for the full minute. ``` Sprites CPU 1,000 × 20 s / 3,600 × $0.07 = $0.39 Memory 1,000 × 60 s / 3,600 × 4 × $0.04375 = $2.92 Total $3.31 Northflank CPU 1,000 × 60 s / 3,600 × 2 × $0.01667 = $0.556 Memory 1,000 × 60 s / 3,600 × 4 × $0.00833 = $0.555 Total $1.11 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 ``` A month of 100,000 runs adds up to $330.56 on Sprites, $111.10 on Northflank and $63.89 on Runtime. With both CPUs busy for the whole minute, it is $1.11 on Northflank, $1.33 on Runtime and $5.25 on Sprites, so for code that never pauses Northflank's allocated rate is the cheapest. A Sprite using just 1 GB would pay $1.12 for the waiting job. Plan fees, storage, network and free allowances are left out. ## Which one to pick - **Fly Sprites**, if each agent should own a lasting machine: a 100 GB disk that is cheap to keep while the Sprite sleeps, and checkpoints of the filesystem that take about a second. - **Northflank**, for CPU-bound jobs, GPUs as large as H100, or sandboxes placed in your own AWS, GCP, Azure or Oracle account. - **Runtime**, for agents that wait on a model: the lowest price of the three for that pattern, a pause that keeps memory and processes, and forks of a running sandbox. ## Moving to Runtime A Sprite you address by name maps to a named Runtime sandbox, which is woken if paused and created if it does not exist yet: ```python check from withruntime import Sandbox dev = Sandbox.get_or_create("agent-42", idle_pause_seconds=300) dev.exec("git pull || true") ``` Other Sprites calls port directly: `client.createSprite(name)` is `Sandbox.create()` and `sprite.execFile(cmd, args)` is `exec([cmd, ...args])`. On Northflank, the service and deployment plan disappear into one create call. `npx withruntime compare --from fly` or `--from northflank` reprices past usage; `npx withruntime switch --from fly` before the first top-up adds matching credit, up to $100. A coding agent can make the change from the one instruction in [migration](/docs/migrate), on a branch and on the free trial. See [Runtime vs Fly.io](/docs/fly-alternative) and [Runtime vs Northflank](/docs/northflank-alternative). ## Sources Rates checked 23 September 2026; the Sprites, Sprites lifecycle and Northflank sandbox pages read 25 September 2026. - [Fly.io pricing](https://fly.io/pricing/), [Sprites](https://fly.io/sprites/), [Sprites lifecycle](https://docs.fly.io/sprites/concepts/lifecycle/) - [Northflank pricing](https://northflank.com/pricing), [Northflank sandboxes](https://northflank.com/product/sandboxes), [Sandboxes on Northflank](https://northflank.com/docs/v1/application/sandboxes/sandboxes-on-northflank) - Runtime [pricing](/docs/pricing) and [Python SDK](/docs/python#sandboxes-by-name) Facts on this page were checked on 25 September 2026.