Modal vs Prime Sandboxes: sandboxes for agent training

Modal and Prime both court reinforcement learning teams. The 2 vCPU, 4 GiB benchmark costs $3.97 on Modal and $1.52 on Prime Sandboxes.

Runtime costs 84% less than Modal and 58% less than Prime for rollouts that wait on a model. In the benchmark, 1,000 one-minute runs of a 2 vCPU, 4 GiB sandbox with 20 CPU-seconds of work each, Modal comes to $3.97, Prime to $1.52 and Runtime to $0.64.

Estimated compute cost

84% less than Modal58% less than Prime Sandboxes

2 vCPUs · 4 GiB · 60 s a run · 20 CPU-seconds busy

Runs1,000

Compute only, at list rates checked 23 September 2026 and 25 September 2026 (Modal pricing, Prime Sandboxes overview). Plan fees, network, taxes and free credits are left out. The worked example below shows the arithmetic.

At a glance

	Modal Sandboxes	Prime Sandboxes	Runtime
Isolation	gVisor, a user-space kernel	Hardware-virtualized microVM, own guest kernel	Firecracker microVM, own kernel
CPU	$0.1419 per physical core-hour (2 vCPUs), request or use	$0.02 per vCPU-hour while running	$0.025 per vCPU-hour of measured CPU, with a small floor
Memory	$0.0240 per GiB-hour, request or use	$0.0125 per GiB-hour	$0.0075 per reserved GiB-hour
Snapshots	Carry state past a session	Listed as coming soon	Pause and forks keep memory and processes
GPUs	Yes	Listed as coming soon	No
At once	Set by plan	1,024 per account to start	100 paid, after 50 in the first week

Training stacks

Modal's argument is one platform: GPU trainers and inference as functions, environments as sandboxes beside them. Prime's is the environment itself at scale and at a low price, microVMs by the thousand on its own compute. Runtime is the environment layer too, billed by use, which suits rollouts that spend most of each step waiting for a policy model to answer.

Cost for the same job

The benchmark in full, 60 seconds a run (one physical core on Modal, Prime's 5 GiB disk):

TextModal     CPU    1,000 × 60 s × 1 core × $0.00003942           = $2.37          Memory 1,000 × 60 s × 4 × $0.00000667                = $1.60          Total                                                  $3.97Prime     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

For a month of 100,000 runs: $396.60 on Modal, $151.67 on Prime, $63.89 on Runtime. When both CPUs stay busy for the whole minute, it is $3.97 on Modal, $1.52 on Prime and $1.33 on Runtime.

Which one to pick

Modal when environments and GPU training should live in one platform.
Prime Sandboxes for a thousand microVMs at once inside Prime Intellect.
Runtime for the lowest price per rollout, forks of a warmed-up environment today, and Harbor and Inspect integrations for eval suites.

See Runtime vs Modal and Runtime vs Prime Sandboxes.

Sources

Modal rates checked 23 September 2026; Prime rates checked 25 September 2026.

Facts on this page were checked on 25 September 2026.