Which is better, Fly Machines or AWS Lambda MicroVMs?
It depends on whether you run on AWS. For agent sandboxes that wait on a model, Runtime is cheapest: $0.64 for the job, against $1.53 on Fly Machines and $4.20 on Lambda, and it keeps memory across pauses for as long as you have credit. Pick Fly Machines for long-running apps in many regions next to Fly's volumes and Postgres. Pick Lambda MicroVMs for sandboxes tied into AWS identity and networking.
At a glance
| Fly Machines | AWS Lambda MicroVMs | Runtime | |
|---|---|---|---|
| Isolation | Firecracker microVM | Firecracker microVM | Firecracker microVM, own kernel |
| Price | performance-2x with 4 GB, $0.0916704 an hour, iad |
$0.2522 an hour for 2 vCPUs and 4 GB | $0.03125 an hour waiting, $0.08 busy, for 2 and 4 GiB |
| Largest | 16 performance vCPUs and 128 GB | Up to 4 vCPUs and 8 GB | 16 vCPUs and 64 GiB, paid |
| Idle | Root disk is temporary; suspend only at 2 GB or less | Suspend keeps memory and disk, up to 8 hours | Pause keeps memory and processes while you have credit |
| Regions | 17 | AWS regions | One US region |
Same hypervisor, about a third of the price
A performance vCPU on Fly is a whole core held for the Machine. Even so, the shape costs about a third of Lambda's per hour. Lambda's premium buys AWS integration and suspend with memory for up to eight hours; Fly Machines suspend only at 2 GB of memory or less.
Cost for the same job
2 vCPU, 4 GiB, 60 seconds a run, 20 CPU-seconds of work, 1,000 runs:
- Size
- 1,000 × 60 s / 3,600 × $0.0916704
- $1.53
- CPU
- 1,000 × 60 s × 2 × $0.0000276944
- $3.32
- Memory
- 1,000 × 60 s × 4 × $0.0000036667
- $0.88
- CPU
- 1,000 × 20 s / 3,600 × $0.025
- $0.14
- Memory
- 1,000 × 60 s / 3,600 × 4 × $0.0075
- $0.50
Both rivals charge by size, so keeping both CPUs busy for the whole minute changes neither: $1.53 on Machines and $4.20 on Lambda, with $1.33 on Runtime.
Which one to pick
- Fly Machines for long-running apps in many regions, alongside Fly's volumes and Postgres.
- Lambda MicroVMs for sandboxes tied into AWS identity and networking.
- Runtime for agent sandboxes at the lowest cost, with memory kept across pauses while you have credit.
See Runtime vs Fly.io and Runtime vs AWS Lambda MicroVMs.
Runtime Cloud
Runtime costs 58% less than a Fly Machine and 85% less than a Lambda MicroVM on the same job. One thousand one-minute runs of a 2 vCPU, 4 GiB sandbox, each with 20 CPU-seconds of work, cost $1.53 on Fly Machines, $4.20 on AWS Lambda MicroVMs and $0.64 on Runtime.
Runtime bills the CPU the code uses, so most of that gap is waiting time you
no longer pay for. Start on the free usage with npx withruntime login; code
that calls Fly's Machines API moves by the migration guide.
Sources
Fly.io prices checked 25 October 2026.
Fly Machines rates checked 25 October 2026; Lambda MicroVMs rates checked 25 October 2026.
Facts on this page were checked on 26 October 2026.