Agent 37 Cloud vs Modal Sandboxes

Agent 37 Cloud

Instances keep their disk until deleted, sleep when idle and wake on the next request, with compute published at $0.80 a vCPU-month and stable error codes on both APIs. The product launched on 29 September 2026. No status page, OpenAPI file, SDK library or published rate limits were found, and the starter credit needs a card.

Modal Sandboxes

GPU sandboxes at the same per-second rates as the rest of Modal. No REST API, and the JavaScript and Go SDKs are beta.

Agent 37 Cloud

1. Send the key as Authorization: Bearer to api.agent37.com and as X-Agent37-Key to the instance URL. The Bearer form on instance URLs is deprecated
2. Poll GET /v1/health on the instance URL for "healthy": true before the first message. status: running only means the machine is up
3. Check whether error is a string before reading error.code. Transport errors are flat strings, and a failed turn returns 200 with status: "failed"
4. Don't blindly retry an exec that timed out after 13 minutes. The command keeps running, so a retry starts a second copy
5. Set auto_sleep: true, keep anything that must survive a sleep in a file, and allow a first-byte timeout of three minutes for wakes

Modal Sandboxes

1. Pass timeout= when you create a sandbox. The default lifetime is 5 minutes
2. Set block_network=True or a cidr_allowlist for untrusted code
3. Give a sandbox a name so a retried create raises AlreadyExistsError instead of starting a second one
4. Snapshot the filesystem before the 24-hour limit and start a fresh sandbox from it
5. Catch ResourceExhaustedError from Sandbox.create() on SDK 1.6.0 and later