Modal vs Vast.ai

Modal

Scale to zero by default, per-second billing and about one-second container boots. No REST API or OpenAPI spec for deploying or invoking Functions.

Vast.ai

API keys can be limited by permission category and by resource ID, the REST API has a public OpenAPI 3.1 file, and the CLI ships weekly with a skill file for coding agents. Machines belong to independent hosts, prices move with the market, rate-limit thresholds are unpublished, and there is no SLA or free tier.

Modal

1. Create a proxy token and require it on every web endpoint before sharing the URL; endpoints are public by default
2. Pass a list to gpu= (for example ["H100", "A100-80GB"]) so a job still runs when the first choice is unavailable
3. Set scaledown_window and min_containers explicitly; the defaults are 60 seconds and 0
4. Use .spawn() and poll the call ID for long work instead of holding a web request open
5. Keep web endpoint traffic under 200 requests a second or ask Modal to raise the limit

Vast.ai

1. Create a scoped key with vastai create api-key --permissions for the agent. A default key has full account access, billing and key management included
2. Pass --raw on every CLI command for JSON output, and -y on vastai destroy instance, which otherwise waits for a confirmation prompt
3. Register an SSH key with vastai create ssh-key before creating an instance, or the host is unreachable
4. Destroy instances when finished. A stopped instance still bills storage, and a zero balance without a saved card leads to deletion
5. Back off on HTTP 429 yourself when calling REST directly. The CLI retries 429 three times from 0.15 seconds
6. Filter searches with verified=true or the Secure Cloud option for sensitive data, and set a dph_total price cap