# Fly Machines vs Prime Sandboxes: two cheap microVMs

A Fly Machine and a Prime sandbox are both microVMs billed while they run. For 1,000 one-minute 2 vCPU runs, Fly costs $1.44 and Prime $1.52.

**Runtime runs the same work for 55% less than a Fly Machine and 58% less than
Prime.** The benchmark is a 2 vCPU, 4 GiB sandbox for 60 seconds with 20
CPU-seconds of work, 1,000 times: $1.44 on Fly Machines, $1.52 on Prime
Sandboxes and $0.64 on Runtime.

## At a glance

|           | Fly Machines                                       | Prime Sandboxes                                | Runtime                              |
| --------- | -------------------------------------------------- | ---------------------------------------------- | ------------------------------------ |
| Isolation | Firecracker microVM                                | Hardware-virtualized microVM, own guest kernel | Firecracker microVM, own kernel      |
| Price     | `performance-2x` with 4 GB, $0.0861 an hour, `iad` | $0.091 an hour for 2 vCPUs, 4 GiB, 5 GiB disk  | $0.03125 an hour waiting, $0.08 busy |
| Largest   | 16 performance vCPUs and 128 GB                    | 16 vCPUs, 64 GiB, 128 GiB of disk              | 16 vCPUs and 64 GiB, paid            |
| State     | Volumes keep files; suspend at 2 GB or less        | Snapshots listed as coming soon                | Pause keeps memory and processes     |
| Regions   | 18                                                 | Not stated                                     | One US region                        |

## Nearly the same hourly price

At 2 vCPUs and 4 GB the two differ by half a cent an hour. Fly's performance
vCPUs are whole cores and its Machines sit in 18 regions; Prime's rate is
promised only through 22 December 2026 but comes with room for a thousand
sandboxes at once. Neither discounts an idle core, which is where Runtime's
measured CPU saves most.

## Cost for the same job

2 vCPU and 4 GB, 60 seconds, 20 CPU-seconds, 1,000 runs; Prime's 5 GiB disk
included:

```
Machines  Size   1,000 × 60 s / 3,600 × $0.0861                = $1.44

Prime     CPU    1,000 × 60 s / 3,600 × 2 × $0.02              = $0.67
          Memory 1,000 × 60 s / 3,600 × 4 × $0.0125            = $0.83
          Disk   1,000 × 60 s / 3,600 × 5 × $0.0002            = $0.02
          Total                                                  $1.52

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
```

Both bill by allocation, so with both CPUs busy for the whole minute they stay at $1.44 on Machines and $1.52 on Prime, while the job costs $1.33 on Runtime.

## Which one to pick

- **Fly Machines** for apps in many regions with Fly's volumes and Postgres.
- **Prime Sandboxes** for RL training at large parallelism.
- **Runtime** for the lowest bill at any load, with memory kept across
  pauses.

See [Runtime vs Fly.io](/docs/fly-alternative) and
[Runtime vs Prime Sandboxes](/docs/prime-sandboxes-alternative).

## Sources

Fly Machines rates checked 23 September 2026; Prime Sandboxes rates checked 25 September 2026.

- [Fly.io pricing](https://fly.io/pricing/)
- [Prime Sandboxes overview](https://docs.primeintellect.ai/sandboxes/overview), [Prime Sandboxes launch](https://www.primeintellect.ai/blog/sandboxes)
- Runtime [pricing](/docs/pricing)

Facts on this page were checked on 25 September 2026.