Runtime changelog, 15 October 2026

What shipped in Runtime Cloud on 15 October 2026: dockerfiles read more like Docker reads them; and containers from slow registries start.

Dockerfiles read more like Docker reads them

An ENV now beats an ARG of the same name in RUN, an ARG with no value stays unset (so ${FOO:-default} gives the default), quotes and \$ keep $ literal in COPY and ARG, and COPY --chmod takes symbolic modes such as a+x. COPY --from naming its own stage is refused with a clear message. See Custom images.

Containers from slow registries start

Reading a container's image allows 5 seconds for each request rather than for the whole read, accepts index.docker.io and registry.hub.docker.com as Docker Hub, and refuses an image built only for arm64 at create instead of failing later.