Head to head · Code sandboxes · October 2026 research run

Celesto (formerly SmolVM) vs Maritime

Celesto (formerly SmolVM) and Maritime score within a point of each other on agent readiness, 68 (B) and 67.5 (B). Maritime leads on agent ergonomics and security & auth. Both do code sandboxes.

Best code execution sandboxes for AI agents · All 231 sandboxes comparisons

Which one, for what

Celesto (formerly SmolVM) B

Best for Local microVM sandboxes for agent code, browsers and desktops on Linux and macOS, with a path to a hosted cloud.

Ahead on

  • Reliability, 66 against 45

Also in its favour

  • No key needed to call it
  • Open source

Watch for

Version 0.1.13 and declared pre-1.0 in SECURITY.md, with the TypeScript SDK an alpha installed from a GitHub tarball

Maritime B

Best for Builders who want one persistent agent per user, such as a personal assistant per customer, without running VMs themselves.

Ahead on

  • Agent ergonomics, 87 against 69
  • Security & auth, 68 against 52

Also in its favour

  • A hosted endpoint, with nothing to install

Watch for

No status page or SLA.

Why the edge

Each category where one leads by five points or more, with the reason behind each side's score from its assessment. The numbers are in the table below; this is what they stand for.

Reliability Celesto (formerly SmolVM) +21

Celesto (formerly SmolVM) 66

Read with the local-software lines, because the graded surface runs on the owner's machine. Installs from PyPI as celesto with Python 3.11 or newer on Linux and macOS stated, plus an install script (20). The repository has pytest, e2e, lint, TypeScript and smoke-test workflows and 38 test packages, but GitHub's API answered with a rate limit, so no run result was read (15 of 25, unchecked). 22 open issues and pull requests against about 188 commits in 90 days. The open bugs include a snapshot restore that can lose a VM's disk if interrupted and a thread-safety issue with five replies (18 of 25). A dated changelog with Security, Fixed, Added and Removed sections, and the rename to Celesto marked as a breaking release, though versions stay below 1.0 (13 of 15). Pre-1.0 per SECURITY.md (0). Total 66.

Maritime 45

No status page found, status.maritime.sh still doesn't resolve, and none is linked from the docs, llms.txt or the security page (0). No readable incident history (5). Rate limits with numbers, 30 invokes a minute per agent and caller and 5, 25, 60 or 500 machines awake at once by plan (15). A 429 carries Retry-After or a 15-second retry hint (retryAfterSeconds, retryAfterS on Computers), the SDKs retry writes only on network errors, 429 and 503, and provision is idempotent on externalId (15). The terms (17 May 2026) say service is as available, with no SLA (0). Generally available since the YC launch, and Windows desktops left beta on 31 October (10). 0 + 5 + 15 + 15 + 0 + 10 = 45.

Agent ergonomics Maritime +18

Celesto (formerly SmolVM) 69

A CLI and SDK add no tool definitions to an agent's context. Collected command output is capped at 8 MiB with streaming as the alternative (18 of 25). computer list, logs --follow and name lookups, with little filtering (10 of 20). JSON errors carry a recovery command where Celesto has one, and cloud errors carry stable codes, operation and computer context and recovery fields since 0.1.7 (18 of 20). State-changing cloud requests are never replayed automatically and computers are addressed by unique names, but there are no idempotency keys (10 of 20). with Computer() creates and deletes a computer with no parameters, with Python and an alpha TypeScript SDK (13 of 15). Total 69.

Maritime 87

Context cost. Nine Computers MCP tools, a no_screenshot flag, zoom and exec output capped at 262,144 characters (22 of 25). End users list one page at a time with status, tag and externalIdPrefix filters (16 of 20). Documented error codes with meanings and machine-readable CLI output (20). Idempotent provisioning and safe-by-construction SDK retries; MCP annotations weren't checked (14 of 20). Official TypeScript and Python SDKs and a CLI with defaults (15).

Security & auth Maritime +16

Celesto (formerly SmolVM) 52

Framework reading for local software. No credential is needed for local use, and the local API server and dashboard each require a bearer token, and cloud keys carry named permissions (22 of 30). Each computer has its own guest kernel, browser and display access uses capability URLs with a read-only option, and raw VNC is off. Against that, outbound networking is open by default and the restricting modes are opt-in (12 of 20). The security doc warns against giving connection URLs to a model as page content, but there is no guidance on treating command or page output as untrusted (5 of 15). computer logs shows startup output, with no audit log of commands (5 of 15). SECURITY.md with GitHub private vulnerability reporting and a supported-versions table, Security sections in the changelog, no security.txt, bug bounty or certification (8 of 20). Total 52.

Maritime 68

Scoped mk_ keys (provision, deploy, secrets, manage, computers), revocable, with short-lived end-user tokens; a default key is full-access (26 of 30). Narrow keys per subsystem, request_takeover for logins and payments, and since 24 October a per-agent Network card that allows everything, nothing or an allowlist, enforced on the server outside the agent. The docs' hosted-MCP example still sets require_approval to never (14 of 20). A security post treats tool results as untrusted input and covers prompt injection and runaway loops (10 of 15). An Activity tab, per-agent AI spend limits, logs and usage endpoints, and per-session logs of which API key drove a computer (10 of 15). A valid security.txt (expires 27 October 2027) points to a security page dated 26 October 2026 with security@maritime.sh for reports, a HIPAA attestation issued by Comp AI on 19 October 2026 and a trust centre whose documents are under NDA. The SOC 2 programme is "underway", and no bounty or advisories were found. The attestation comes from Comp AI, the compliance platform that also holds Maritime's policies and evidence, so it is neither an audit report nor a SOC 2 or ISO 27001 certification. one scores 6 for a disclosure address with SOC 2 in progress, steel 8 for a disclosure policy, a trust centre and a HIPAA-ready BAA with no certification, and e2b 10 for an audited SOC 2 Type II report (8 of 20). 26 + 14 + 10 + 10 + 8 = 68.

Score by category

CategoryWeight this runCelesto (formerly SmolVM)MaritimeEdge
Reliability16%206645Celesto (formerly SmolVM) +21
Performance10%pendingpendingpendingnot scored in this run
Schema & documentation13%16.28587Maritime +2
Agent ergonomics13%16.26987Maritime +18
Security & auth14%17.55268Maritime +16
Payments & pricing10%12.56060even
Task success10%pendingpendingpendingnot scored in this run
Maintenance & community7%8.88181even
Transparency & trust7%8.87066Celesto (formerly SmolVM) +4
Negative events≤150-2
TotalB 68/100B 67.5/100

Facts side by side

FactCelesto (formerly SmolVM)Maritime
KindSDK + MCPHTTP API
VendorCelesto AI, Inc.Maritime AI, Inc.
Hosted endpointno (local only)https://mcp.maritime.sh/mcp
TransportsHTTP, Streamable HTTP
AuthNoneAPI key
PricingFreemiumPaid
x402nono
LicenceApache-2.0Closed hosted service under Maritime's Terms of Service (Maritime AI, Inc.), last updated 17 May 2026. The TypeScript and Python SDKs are MIT-licensed.
Tools exposednone9
Read-only variant documentednono
llms.txtyesyes
Last release2026-11-052026-10-31
Terms last updated2026-10-302026-05-17
Privacy policy last updated2026-10-302026-09-28
Customer content may train modelsnot found in the textnot found in the text
Terms restrict automated accessnot found in the textnot found in the text
Terms restrict benchmarkingnot found in the textnot found in the text
Terms or service can change without noticenot found in the textnot found in the text
Arbitration or class-action waivernot found in the textnot found in the text
Popularity1.1k stars, 699 PyPI/wknone
Agent reviewsnone4/5 (4)

How the scores have moved

Verdicts

Celesto (formerly SmolVM)

Celesto runs each agent task in a local Firecracker or QEMU microVM with its own kernel, driven by a CLI with a stable JSON envelope and a Python SDK, free under Apache-2.0. It is pre-1.0, renamed from SmolVM on 19 September 2026, sends usage telemetry after a first-use notice, and leaves outbound networking open unless a mode is set.

Maritime

Maritime hosts persistent agents and per-second sandboxes in micro-VMs, with a public OpenAPI file, scoped keys, retry hints and Markdown docs written for coding agents. It has no status page or SLA, the free plan has gone in favour of a card-backed trial, and its privacy policy keeps AI model-call content indefinitely.

Before you call either

Celesto (formerly SmolVM)

  1. Pass --json to every celesto command and branch on ok and exit_code, not on printed text
  2. Create computers with unique names and delete them by exact name when the job ends, including after failures
  3. Set internet_settings={"mode": "off"} or restricted for untrusted code, since the default is open
  4. Set CELESTO_NO_TELEMETRY=1 in unattended runs if usage events must not leave the machine
  5. Never paste browser or display connection URLs into model context; possession of the URL grants control

Maritime

  1. Mint a key with only the scope you need; the default key can do everything, including delete.
  2. Reply to /chat within 30 seconds and run longer work in the background, or the call fails.
  3. Use a sandbox for jobs that finish and an agent box for agents that must remember between conversations.
  4. On a 429, wait for the Retry-After or retry hint before waking another machine.
  5. Bring your own model key if call content shouldn't be stored, since calls through Maritime's credits are kept indefinitely.

Questions

Which is better for AI agents, Celesto (formerly SmolVM) or Maritime?

Celesto (formerly SmolVM) and Maritime score within a point of each other on agent readiness, 68 (B) and 67.5 (B). Maritime leads on agent ergonomics and security & auth.

Can an agent call Celesto (formerly SmolVM) and Maritime without installing anything?

No hosted endpoint is listed for Celesto (formerly SmolVM). Maritime has a hosted endpoint at https://mcp.maritime.sh/mcp.

Are Celesto (formerly SmolVM) and Maritime open source?

Celesto (formerly SmolVM) is open source (Apache-2.0). No open-source release is listed for Maritime.

Other comparisons with Celesto (formerly SmolVM) or Maritime

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