Celesto vs Modal
Celesto vs Modal: Celesto gives every agent a persistent virtual machine with a desktop, CDP browser, and shell for 87% less per running hour on the same CPU and memory, while Modal Sandboxes are gVisor containers by default that start in under a second, run up to 24 hours, and add GPUs, snapshots, and domain egress rules.
Pick by how long the agent's machine lives: a computer that stops, starts, and keeps its disk favors Celesto; short-lived sandboxes next to GPU workloads already on Modal favor Modal.
- Same 2 vCPU · 4 GB sandbox
- $0.030 vs $0.238
- Per running hour at Modal's Sandbox rates. 87% or more less on every matched size.
- Sandbox lifetime
- Persistent
- Celesto sandboxes stop and start with their disk. Modal Sandboxes default to 5 minutes and run at most 24 hours.
- Isolation by default
- Virtual machine
- Every Celesto sandbox is a KVM VM. Modal defaults to gVisor, with a VM runtime available.
Persistent VMs with a shell and browser, not 24-hour containers.
A dot marks whoever has the edge on that line.
Isolation and access
- Isolation model
- Its own KVM virtual machine and kernel(Celesto has the edge)
- gVisor by default; a KVM VM runtime is available
- Cold boot
- Under 2 seconds
- Sub-second, per its product page(Modal has the edge)
- Shell access
- Browser terminal, or celesto computer ssh with no SSH keys(Celesto has the edge)
- modal shell into a running Sandbox; SSH only by running sshd behind a TCP tunnel
- Docker inside
- Supported
- On the VM runtime, by starting dockerd
Browser and desktop
- Desktop view
- Live desktop on the browser templates, read-only or with control(Celesto has the edge)
- VNC example on the VM runtime, built with Xvfb and noVNC
- Browser over CDP
- Built-in Chromium at a CDP URL(Celesto has the edge)
- No CDP endpoint found; Playwright in an example
State and storage
- Lifetime
- Persistent; stop and start keep the disk(Celesto has the edge)
- 5 minutes by default, up to 24 hours
- Snapshots
- Stop and start keep disk and packages; processes end
- Filesystem and directory snapshots; memory snapshots in alpha(Modal has the edge)
- Disk
- 20 to 100 GB by size, included
- Volumes and bucket mounts; 512 GiB root on the VM runtime
Network and tools
- Egress control
- Internet on or off (TypeScript SDK)
- Block all, CIDR allow lists, domain allow list (beta)(Modal has the edge)
- Public ports
- Up to 4 public HTTPS ports per sandbox
- Encrypted and raw TCP tunnels; custom domains on Team(Modal has the edge)
- MCP
- Hosted MCP server that creates sandboxes and runs commands(Celesto has the edge)
- No MCP server for Sandboxes found
- SDKs and API
- Python, TypeScript, CLI, and a REST API
- Python, plus JavaScript and Go in beta; CLI; gRPC API
Price and limits
- 2 vCPU · 4 GB, per hour
- $0.030(Celesto has the edge)
- $0.238
- GPUs
- No GPU sizes
- GPU Sandboxes on gVisor(Modal has the edge)
- Free usage
- $5 one-time credit, no card
- $30 a month on Starter(Modal has the edge)
- Running at once
- Up to 10
- 100 containers on Starter(Modal has the edge)
Celesto has the edge Modal has the edge
87% less per hour on every matched size.
Each Celesto size next to the same CPU and memory on Modal, or its nearest size, per hour.
| Hardware | Modal | Celesto |
|---|---|---|
| 1 vCPU · 2 GB | $0.119/hour | $0.015/hourMicro, 20 GB disk included |
| 2 vCPU · 4 GB | $0.238/hour | $0.030/hourStandard, 30 GB disk included |
| 2 vCPU · 8 GB | $0.334/hour | $0.040/hourMemory, 40 GB disk included |
| 4 vCPU · 16 GB | $0.668/hour | $0.080/hourLarge, 60 GB disk included |
| 8 vCPU · 32 GB | $1.336/hour | $0.160/hourXL, 100 GB disk included |
Modal prices use its Sandbox rates, which are about three times its Function rates, with one physical core counted as 2 vCPU. Region and non-preemptible multipliers are not applied. Celesto prices include the root disk.
Long-lived agent machines run cheaper on Celesto.
Choose Celesto if
- You want to pay 87% less per running hour for the same CPU and memory
- The agent's machine should live for days and keep its disk across stops
- Your agent needs a desktop and a CDP browser without building them
- You want a shell and terminal without setting up sshd and a tunnel
- Claude Code, Cursor, or another MCP client should drive sandboxes
Choose Modal if
- Your sandboxes sit next to GPU workloads already running on Modal
- You need GPUs inside the sandbox
- You start many sandboxes at once and each one finishes within 24 hours
- You need egress allow lists by CIDR or domain
- Boot time in milliseconds, rather than under 2 seconds, matters to your workload
Questions.
Can you SSH into a Modal Sandbox?
Modal's docs offer modal shell to open a shell in a running Sandbox and Sandbox.exec with a PTY. For real SSH, the documented route is installing and running sshd yourself and exposing port 22 through an experimental unencrypted TCP tunnel, shown for Function containers rather than Sandboxes. Celesto gives you celesto computer ssh with no keys or open port, and a terminal in the browser console.
Is Celesto cheaper than Modal?
Yes, on list price. Modal prices Sandboxes at $0.00003942 per physical core-second and $0.00000667 per GiB-second, about three times its Function rates, which is $0.238 an hour for 2 vCPU and 4 GiB. Celesto Standard has the same CPU and memory for $0.030 an hour with a 30 GB disk included, at least 87% less on every matched size. Modal Starter includes $30 of usage a month.
How long can a Modal Sandbox run?
Modal Sandboxes default to a 5-minute lifetime and accept a timeout of up to 24 hours; Modal recommends filesystem snapshots to continue past that. Celesto sandboxes are persistent: stop one and start it later with its disk, installed packages, and CelestoFS workspace intact, for 30 days after a stop.
How are Celesto and Modal sandboxes isolated?
Every Celesto sandbox is its own KVM virtual machine with its own kernel. Modal Sandboxes run on gVisor, which handles system calls in user space, by default, and offer a VM runtime isolated by KVM.
Can my agent use a browser in Celesto or Modal?
Celesto's browser-agent template includes a Chromium browser your code drives over CDP by calling computer.browser(), and a live desktop view. Modal publishes an example that builds Xvfb, x11vnc, noVNC, and Playwright on its VM runtime; no CDP endpoint is documented.
What is a good Modal alternative for AI agent sandboxes?
Celesto is a Modal alternative when agents need a long-lived computer: each sandbox is its own virtual machine with a terminal, desktop view, CDP browser, public preview URLs, Docker, and a disk that survives stops, from $0.015 per hour, with a hosted MCP server. New accounts get a one-time $5 credit with no card.
Start with $5 in credits. No card required.
Modal details from its public pricing and documentation, as of October 17, 2026: Pricing · Sandboxes · Sandbox reference · modal shell · modal.forward · Networking · VNC example. Celesto details come from the current sandbox catalog and feature list. Prices are list rates, not measured performance. Modal is a trademark of its owner; Celesto is not affiliated with it.