What is the best alternative to Prime Sandboxes?
It depends on whether your rollouts need memory kept between steps, since Prime's checkpoints and forks save the filesystem only. For rollouts that wait on a policy model, Runtime has the lowest bill: $0.64 for the job below against $1.52 on Prime. It also forks a running environment with its memory and processes. If room for 1,024 sandboxes in parallel matters most, Prime is hard to beat. Pick Modal to keep sandboxes beside GPU training code, and Morph to branch into hundreds of replicas.
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. Checkpoints and forks save a sandbox's filesystem only: processes start fresh and nothing in memory carries over. Branching a warm environment, with its processes running, into several rollouts needs more than that.
- 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 fourth. Pricing shows each row's arithmetic without plan fees, idle storage, network or credits.
| # | Provider | Isolation | CPU billed on | 1,000 runs |
|---|---|---|---|---|
| 1 | Runtime Cloud | 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 | Prime Sandboxes (5 GiB disk) (the one you are replacing) | microVM, own guest kernel | Allocated vCPUs while running | $1.52 |
| 5 | Fly Machines, performance-2x with 4 GB |
Firecracker microVM | The machine's size while started | $1.53 |
| 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 | Fly Sprites (4 GB in use) | Firecracker microVM | Measured CPU | $2.40 |
| 10 | CodeSandbox SDK, a Nano VM | Firecracker microVM | The VM's size, by the minute rounded up | $2.48 |
| 11 | E2B | Firecracker microVM, own kernel | Allocated vCPUs | $2.76 |
| 12 | Daytona | Containers by default; VM class separate | Allocated vCPUs | $2.76 |
| 13 | Blaxel (4 GB) | Lightweight virtual machines | Included with memory, active time | $3.45 |
| 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:
- CPU
- 1,000 × 20 s / 3,600 × $0.025
- $0.14
- Memory
- 1,000 × 60 s / 3,600 × 4 × $0.0075
- $0.50
- 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
- CPU
- 1,000 × 60 s / 3,600 × 2 × $0.01667
- $0.556
- Memory
- 1,000 × 60 s / 3,600 × 4 × $0.00833
- $0.555
- CPU
- 1,000 × 60 s × 1 core × $0.00003942
- $2.37
- Memory
- 1,000 × 60 s × 4 × $0.00000667
- $1.60
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. Northflank: the lowest allocated rates
$0.01667 per vCPU-hour and $0.00833 per GB-hour, $1.11 for this job, and GPUs billed by the second. Each sandbox is a service with a deployment plan.
2. Modal Sandboxes: GPUs beside the training code
gVisor rather than a microVM, with CPU billed on the larger of request and use, $3.97 here. Modal's draw is running sandboxes next to GPU functions on one platform.
3. Morph: branching at scale
$0.05 per MCU-hour, and Infinibranch forks a running machine, memory included, into hundreds of replicas.
4. Daytona: GPUs and a large free start
E2B's rates, $2.76 here, with GPU sandboxes and $200 of free compute.
Runtime Cloud
Runtime runs the same job for 58% less than Prime Sandboxes. The 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. At 100,000 runs a month, the costs are $63.89 and $151.67, so Runtime is first in the table above. 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 October 2026; the others checked 25 October 2026.
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. Memory is billed at $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 while you have credit, and a fork turns one running environment into up to 100 copies. The Harbor and Inspect integrations run eval suites, Terminal-Bench among them.
A first rollout costs nothing to try: sign in with npx withruntime login.
For an existing environment, the section below and the
migration guide lay out the port.
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() 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 26 October 2026; Northflank, Modal, Morph and Daytona rates checked 25 October 2026.