Prime Sandboxes alternatives: agent sandboxes ranked by cost

Runtime is the cheapest Prime Sandboxes alternative for rollouts that wait on a model: 58% less per job, with forks today.

Runtime runs the same job for 58% less than Prime Sandboxes. 1,000 one-minute runs of a 2 vCPU, 4 GiB sandbox, each busy for 20 CPU-seconds, cost $0.64 on Runtime and $1.52 on Prime, or $63.89 against $151.67 at 100,000 runs a month. Prime's CPU rate is the lowest of any allocated provider here, but it bills every vCPU for the whole run. Prime rates checked 25 September 2026; the others checked 23 September 2026.

Why compare Prime Sandboxes with others?

Prime Intellect built its sandboxes for agentic reinforcement learning: hardware-virtualized microVMs, room for 1,024 per account, and rates it calls the most competitive on the market. Three things still send teams to compare:

• Rollouts mostly wait. A policy model thinks while the environment idles. Prime bills the vCPUs, memory and disk a sandbox was given while it runs, so the idle time is charged in full.
• State between steps. Saving, restoring and forking a sandbox mid-run are listed as coming soon. Branching an environment into several rollouts, or keeping one warm between training steps, needs them today.
• Launch pricing. The published rates hold through 22 December 2026. A budget planned past that date has no published figure to plan on.

Which alternatives are cheapest?

Sixteen rows, one job: 1,000 runs of 60 seconds on a 2 vCPU, 4 GiB sandbox with 20 CPU-seconds of work each. Prime lands fifth. Pricing shows each row's arithmetic without plan fees, idle storage, network or credits.

#	Provider	Isolation	CPU billed on	1,000 runs
1	Runtime	Firecracker microVM, own kernel	Measured CPU, with a small floor	$0.64
2	Northflank	microVMs for CPU work, gVisor for GPU work	Allocated vCPUs	$1.11
3	Cloudflare Sandbox (2 vCPU, 6 GiB, 12 GB disk)	A container in its own VM	Active CPU	$1.35
4	Fly Machines, performance-2x with 4 GB	Firecracker microVM	The machine's size while started	$1.44
5	Prime Sandboxes (5 GiB disk) (the one you are replacing)	microVM, own guest kernel	Allocated vCPUs while running	$1.52
6	Morph, 2 MCUs	Full virtual machines	The machine's size in MCUs	$1.67
7	Vercel Sandbox, iad1 (4 GB)	Firecracker microVM, own kernel	Active CPU	$2.12
8	Freestyle (32 GiB disk)	Full Linux virtual machines	Allocated vCPUs	$2.25
9	CodeSandbox SDK, a Nano VM	Firecracker microVM	The VM's size, by the minute rounded up	$2.48
10	E2B	Firecracker microVM, own kernel	Allocated vCPUs	$2.76
11	Daytona	Containers by default; VM class separate	Allocated vCPUs	$2.76
12	Blaxel (4 GB)	Lightweight virtual machines	Included with memory, active time	$2.76
13	Fly Sprites (4 GB in use)	Firecracker microVM	Measured CPU	$3.31
14	Modal Sandboxes (1 physical core)	gVisor, a user-space kernel	Requested or used, whichever is higher	$3.97
15	AWS Lambda MicroVMs, Arm	Firecracker microVM	Baseline vCPUs while running	$4.20
16	Runloop, a MEDIUM devbox	microVM, with a container inside	Allocated CPUs while running	$5.33

Cost for the same job

Runtime, Prime, Northflank (the only allocated provider cheaper than Prime) and Modal (a common choice for RL research) in full:

TextRuntime     CPU    1,000 × 20 s / 3,600 × $0.025          = $0.14            Memory 1,000 × 60 s / 3,600 × 4 × $0.0075     = $0.50            Total                                            $0.64Prime       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                                            $1.52Northflank  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                                            $1.11Modal       CPU    1,000 × 60 s × 1 core × $0.00003942    = $2.37            Memory 1,000 × 60 s × 4 × $0.00000667         = $1.60            Total                                            $3.97

If the rollout kept both CPUs busy for the whole minute, the job would cost $1.33 on Runtime, $1.52 on Prime, $1.11 on Northflank and $3.97 on Modal. Prime charges the same either way; Runtime's figure rises with the work and still comes in under Prime's, because Runtime's memory is $0.005 a GiB-hour cheaper.

The alternatives, for a Prime Sandboxes user

1. Runtime: measured CPU and forks today

Each sandbox is a Firecracker microVM with its own kernel. CPU is $0.025 per vCPU-hour of measured use, never below a twentieth of a vCPU, and memory $0.0075 per reserved GiB-hour. A paid sandbox takes up to 16 vCPUs and 64 GiB, the same ceiling as Prime. Pause keeps memory and processes for 1 to 365 days, and a fork turns one running environment into up to 10 copies. The Harbor and Inspect integrations run eval suites, Terminal-Bench among them.

2. Northflank: the lowest allocated rates

$0.01667 per vCPU-hour and $0.00833 per GB-hour, $1.11 for this job, and GPUs by the hour. Each sandbox is a service with a deployment plan.

3. Modal Sandboxes: GPUs beside the training code

gVisor rather than a microVM, CPU on the larger of request and use, $3.97 here. Modal's pull is running sandboxes next to GPU functions in one platform.

4. Morph: branching at scale

$0.05 per MCU-hour, and Infinibranch forks a running machine, memory included, into hundreds of replicas.

5. Daytona: GPUs and a large free start

E2B's rates, $2.76 here, with GPU sandboxes and $200 of free compute.

Moving rollouts to Runtime

Set the environment up once, then fork it for each rollout so none of them repeats the install:

Pythonfrom withruntime import Sandboxwith Sandbox.create(funding="paid") as env:    env.exec("pip install --quiet gymnasium")    rollouts = env.fork(count=8)  # eight running copies, memory included    for rollout in rollouts:        print(rollout.exec("python3 -c 'import gymnasium; print(gymnasium.__version__)'").stdout)        rollout.stop()

Harbor and Inspect users can switch the environment instead of the code: Harbor and Inspect. For the full picture read Runtime vs Prime Sandboxes, or price a rollout in the Prime Sandboxes pricing calculator.

Sources

Prime Sandboxes checked 25 September 2026; Northflank, Modal, Morph and Daytona rates checked 23 September 2026.

• Prime Sandboxes overview, Prime Sandboxes launch
• Northflank pricing
• Modal pricing
• Morph Cloud pricing, Daytona pricing
• Runtime pricing