A limit without credit says plainly how to lift it
Every refusal an account meets because it has not paid (sizes, sandboxes at once, builds, used-up included usage, public previews, open ports and the network features) now answers in one shape: what was refused and the limit, what to do now, and that the account's owner adds credit at Usage & billing, with the welcome match. details.addCredit says the same for code. See responses and errors.
Out-of-memory kills are reported
When Linux ends a program because its sandbox ran out of memory, the command's result, its process and the stream's exit event carry outOfMemory: the code out_of_memory, how many processes were ended, the sandbox's memoryMiB and a hint (1,024 MiB or more, or a resize while paused). Each such command also sends the event sandbox.out_of_memory to your webhooks. See when a program runs out of memory.
Rebuilt custom images start warm from their first sandbox
A new build of an image starts at the sizes your account's other images use on that server, before any sandbox asks for them; only your own account's images count. On a test server, a rebuilt image's first 1 vCPU, 512 MiB sandbox started in 120 to 139 ms, where it took 2,364 ms. See fast starts.
Custom images behave as on Docker in three more places
A file the image puts in /tmp is there when a sandbox starts; a string command on an image without bash, such as Alpine or BusyBox, runs under /bin/sh; and 0.0.0.0 and the sandbox's own addresses skip the proxy, so a server you start in the sandbox answers from inside it. Existing images get this at their next cold start, with no rebuild. See images.
A secret goes only into a request header
The proxy puts a secret's value in the header you set for it, or, with none set, in the credential headers (Authorization, x-api-key, x-goog-api-key, api-key, xi-api-key, x-subscription-token and private-token), never in a URL's path or query or another header, where the placeholder now goes out as it is. Stored OpenAI, Anthropic and Gemini keys keep working; code that put a placeholder in a URL should send it in a header. See secrets sandboxes never see.
A full disk answers no_space with how to free it
A command, file write or other call that finds the sandbox's disk full answers 409 no_space, with a hint: delete files, or create a sandbox with a larger diskMiB. The sandbox keeps taking commands, so the rm that frees space runs. See troubleshooting.