Runtime costs 58% less than a Fly Machine for an agent that waits on a model. 100,000 one-minute runs of a 2 vCPU, 4 GiB sandbox, each using 20 CPU-seconds, cost $63.89 a month on Runtime and $152.78 on Fly Machines. Both run Firecracker microVMs. A Machine bills its whole size while started, and Runtime bills the CPU your code uses. Rates checked 25 October 2026.
How Fly Machines bill
Fly sells Machines in fixed sizes, priced by the hour while the Machine is
started, by the second. What the CPUs do in that time does not change the
price. The size that matches a 2 vCPU, 4 GiB sandbox is performance-2x with
4 GB, at the rates of Fly's Ashburn (iad) region.
| Size | Fly Machines, iad |
Runtime, same shape |
|---|---|---|
| 2 performance vCPUs and 4 GB | $0.0916704 an hour | $0.03125 an hour waiting, $0.08 fully busy |
| Per minute | $0.001528 | From $0.00052 |
Runtime prices the parts separately: $0.025 per vCPU-hour of measured CPU, with a floor of a twentieth of a vCPU, and $0.0075 per reserved GiB-hour.
Because Fly sells fixed sizes, the calculator prices Fly Machines only at 2 vCPUs and 4 GiB. Choose another shape and it lists Fly Machines as unpriced rather than guessing a size.
Example workloads
A month of each at 2 vCPUs and 4 GiB, CPU and memory only, from the calculator above.
| Workload | Runtime | Fly Machines |
|---|---|---|
| Agent runs: 2 vCPU, 4 GiB, 60 s, 20 CPU-seconds, 100,000 a month | $63.89 | $152.78 |
| Every CPU busy: 2 vCPU, 4 GiB, 60 s, 120 CPU-seconds, 100,000 | $133.33 | $152.78 |
| Waiting agents: 2 vCPU, 4 GiB, 30 min, 180 CPU-seconds, 10,000 | $162.50 | $458.35 |
| Hour-long jobs: 2 vCPU, 4 GiB, 60 min, 6,480 CPU-seconds, 1,000 | $75.00 | $91.67 |
Runtime costs less in all four, including runs that keep both CPUs working the whole time. The more a sandbox waits, the wider the gap: half-hour sessions that use 180 CPU-seconds each cost 62% less on Runtime.
A performance Machine's vCPUs are whole cores kept for it. Runtime's default
CPU is shared, as the figures above assume. cpu: "reserved" keeps every vCPU
for one sandbox and raises its waiting charge (pricing).
What the calculator leaves out
- Plan fees. Fly charges none for Machines; they are pay as you go. Runtime has none either: prepaid credit from $19.
- Storage. A Machine's root disk is temporary. Files that must stay go on Fly Volumes, which the calculator does not price. On Runtime, disk is included while a sandbox runs, and a paused one keeps its files, memory and running processes for $0.08 per GB a month.
- Stopping on time. The figures assume each Machine stops when its run ends. One left started keeps billing its whole size.
- Free credit. Fly's pricing page states none for Machines. Runtime gives 100 free hours of a 1 GB machine in the first 30 days, no card.
Price your own runs exactly
With a few runs on Runtime behind you, price exactly those sandboxes as
performance-2x Machines:
Terminalruntime compare --from fly-machinesIt covers the last 30 days of settled sandboxes (--days up to 90). Moving
from Fly? Credit you add within 30 days of signing up is matched, up to $1,000 in total (welcome match).
Runtime vs Fly.io compares Machines and Sprites with Runtime in full. Fly's agent sandboxes, Sprites, bill differently. Their pricing calculator prices any shape. The sandbox cost calculator sets every provider side by side.
Sources
- Fly.io pricing, checked 25 October 2026
- Runtime pricing
Rival rates on this page were checked on 25 October 2026.