# Fly Machines vs CodeSandbox: pricing, isolation and limits Both sell fixed-size Firecracker VMs; 2 vCPU and 4 GB costs $0.0861 an hour on a Fly Machine and $0.1486 on a CodeSandbox Nano VM. **Runtime runs the same job for 55% less than a Fly Machine and 74% less than CodeSandbox.** 1,000 one-minute runs of a 2 vCPU, 4 GiB sandbox cost $1.44 on Fly Machines, $2.48 on CodeSandbox and $0.64 on Runtime. Both rivals bill a whole machine size for as long as it is up; Runtime bills the CPU your code uses and the memory you chose. Rates checked 23 September 2026. ## At a glance Fly Machines are Fly.io's general-purpose VMs, priced here at the Ashburn (`iad`) rates. CodeSandbox's figures come from Together's documentation of the CodeSandbox SDK; CodeSandbox is a Together company. | | Fly Machines | CodeSandbox SDK | Runtime | | ------------ | ------------------------------------------------------------ | ---------------------------------------------------------- | ------------------------------------------------------- | | Isolation | Firecracker microVM | Firecracker microVM | Firecracker microVM, own kernel | | How it bills | A fixed size per second while started | A fixed size in credits, by the minute rounded up | Measured CPU plus reserved memory, by the second | | 2 vCPU, 4 GB | `performance-2x`, $0.0861 an hour | Nano, 10 credits an hour at $0.01486, $0.1486 | $0.08 an hour fully busy, $0.03125 waiting | | Size range | Up to 16 performance vCPUs and 128 GB | Pico (2 cores, 1 GB) to XLarge (64 cores, 128 GB) | vCPUs and memory chosen per sandbox | | Plan fee | None; pay as you go | Build free with 10 VMs at once; Scale $170 a month for 250 | None; prepaid credit from $10 | | Free start | Not stated on the pricing page | The free Build plan | 50 sandbox hours, no card | | When idle | Root disk is temporary; suspend keeps memory up to 2 GB only | Hibernates after the session disconnects | Pause keeps files, memory and processes, 1 to 365 days | | Start | Cold start about 2 seconds or more, in Fly's words | Launches in under three seconds, in Together's words | 351 ms median to first Python result, 24 September 2026 | ## Which fixed size is cheaper? The Fly Machine, by a wide margin. A `performance-2x` with 4 GB is $0.0861 an hour and a CodeSandbox Nano VM, with the same 2 cores and 4 GB, is $0.1486: about 73% more. CodeSandbox also rounds each VM's time up to the next minute, so a run of 3 minutes 25 seconds is billed as 4. A Fly Machine bills by the second. Neither price moves with the work. A Machine pays its whole size while it is started and a Nano pays 10 credits an hour while it runs, whether the code is compiling or waiting on a model. That is the difference Runtime removes: its CPU charge is measured, with a floor of a twentieth of a vCPU while the sandbox waits. Each sells steps, not shapes. CodeSandbox doubles from Nano to Micro (4 cores, 8 GB) and on up. On Runtime you set `vcpu` and `memoryMiB` for each sandbox and pay for exactly that. ## Cost for the same job 1,000 runs of a 2 vCPU, 4 GiB sandbox. Each run lasts 60 seconds and keeps the CPU busy for 20 CPU-seconds: an agent that mostly waits for a model. The Fly Machine is a `performance-2x` with 4 GB and the CodeSandbox VM is a Nano. ``` Machines Size 1,000 × 60 s / 3,600 × $0.0861 = $1.44 CodeSandbox Size 1,000 × 60 s / 3,600 × $0.1486 = $2.48 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 a month that is $143.50 on Fly Machines, $247.67 on CodeSandbox and $63.89 on Runtime. With both CPUs busy for the whole minute, it is $1.33 on Runtime against $1.44 on Machines and $2.48 on CodeSandbox, so Runtime is cheaper however busy the sandbox is. Each run is a whole minute, so CodeSandbox's rounding adds nothing here; a 40-second run would still pay for a minute there. Plan fees, storage, network and free credits are left out. ## What happens when the machine sits idle? A Fly Machine's root disk is temporary, so files that must survive go on a Fly Volume. Suspend keeps a Machine's whole memory in a Firecracker snapshot and resumes in a few hundred milliseconds, but only for a Machine with 2 GB of memory or less, so the 4 GB size above cannot use it. Fly also says a suspended snapshot is discarded by a deploy, a host migration or maintenance. A CodeSandbox VM hibernates once its session disconnects, and Together says it can resume or clone from a memory snapshot in three seconds. A paused Runtime sandbox keeps its files, memory and running processes at any size, for the retention you set from 1 to 365 days, and wakes by itself on the next request, usually in about half a second. See [how to pause and resume a sandbox](/how-to/pause-and-resume-a-sandbox). ## Which one to pick - **Pick Fly Machines** for long-lived services near users: Machines run in 18 regions, beside Fly Volumes and Managed Postgres in the same account. - **Pick CodeSandbox** for very large VMs, up to 64 cores and 128 GB, or for many VMs on one plan: Scale runs 250 at once. - **Pick Runtime** for agent work that waits more than it computes: measured CPU at $0.025 a vCPU-hour, any size you set, per-second billing, and pause that keeps memory whatever the size. ## Switch from either one Create a Runtime sandbox where you created a Machine or a VM for each job, and stop it when the job ends. Size it to what the job needs rather than to the nearest step: ```ts import { Runtime } from "withruntime"; const runtime = new Runtime(); const sbx = await runtime.sandboxes.create({ vcpu: 2, memoryMiB: 4096, timeoutSeconds: 900 }); try { const run = await sbx.exec(["python3", "-c", "print(6 * 7)"]); console.log(run.exitCode, run.stdout); } finally { await sbx.stop(); } ``` Or give your coding agent the one instruction in [migration](/docs/migrate): it switches the project on a branch, tests it on the free trial and reports the monthly saving. `npx withruntime compare --from fly-machines` (or `--from codesandbox`) prices what you ran at the old provider's rates, and `npx withruntime switch --from fly` before your first top-up matches that top-up with credit, up to $100. The full side-by-sides are [Runtime vs Fly.io](/docs/fly-alternative) and [Runtime vs CodeSandbox](/docs/codesandbox-alternative). ## Sources Rates checked 23 September 2026; the Fly suspend and Together pages read 25 September 2026. - [Fly.io pricing](https://fly.io/pricing/), [Machine suspend and resume](https://docs.fly.io/reference/suspend-resume/), [Fly Volumes](https://fly.io/docs/volumes/overview/), [Fly.io regions](https://fly.io/docs/reference/regions/) - [Together Code Sandbox](https://docs.together.ai/docs/together-code-sandbox), [CodeSandbox SDK pricing](https://codesandbox.io/docs/sdk/pricing) - Runtime [pricing](/docs/pricing) and [speed](/docs/speed) Facts on this page were checked on 25 September 2026.