Fly Sprites vs Prime Sandboxes: measured or allocated

Sprites charge measured CPU and memory in use; Prime charges allocation while running. Memory decides it: $3.31 on Sprites, $1.52 on Prime for the benchmark.

Runtime costs 81% less than Sprites and 58% less than Prime on that benchmark: 1,000 one-minute runs of a 2 vCPU, 4 GiB sandbox with 20 CPU-seconds of work each, which come to $3.31, $1.52 and $0.64.

At a glance

	Fly Sprites	Prime Sandboxes	Runtime
Isolation	Firecracker microVM	Hardware-virtualized microVM, own guest kernel	Firecracker microVM, own kernel
CPU	$0.07 per CPU-hour of measured CPU	$0.02 per vCPU-hour while running	$0.025 per vCPU-hour of measured CPU, with a small floor
Memory	$0.04375 per GB-hour of memory in use	$0.0125 per GiB-hour	$0.0075 per reserved GiB-hour
Lifetime	Persistent, pauses itself; 100 GB disk kept	Default timeout 60 minutes, up to unlimited	Leases extended, persistent, pauses up to 365 days
Built for	A personal computer that stays	RL rollouts by the thousand	Agents and evals

One cheap meter each

Sprites' CPU line is cheap because it is measured; Prime's is cheap because the rate is low. Memory is where Sprites lose, at $0.04375 per GB-hour against Prime's $0.0125. Runtime measures CPU and charges less for memory than both.

Cost for the same job

The benchmark, 60 seconds a run, with 4 GB in use on Sprites and a 5 GiB disk on Prime:

TextSprites  CPU    1,000 × 20 s / 3,600 × $0.07                  = $0.39         Memory 1,000 × 60 s / 3,600 × 4 × $0.04375           = $2.92         Total                                                  $3.31Prime    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                                                  $1.52Runtime  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

If both CPUs were busy for the whole minute, the job would cost $5.25 on Sprites, $1.52 on Prime and $1.33 on Runtime.

Which one to pick

• Fly Sprites for one persistent machine per developer or agent, with a large disk.
• Prime Sandboxes for training runs with thousands of short environments.
• Runtime for the lowest price busy or waiting, and forks today.

See Runtime vs Fly.io and Runtime vs Prime Sandboxes.

Sources

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

• Fly.io pricing, Sprites
• Prime Sandboxes overview, Prime Sandboxes launch
• Runtime pricing

Facts on this page were checked on 25 September 2026.