lix/src/libstore/settings/keep-outputs.md

name, internalName, type, default, aliases

name	internalName	type	default	aliases
keep-outputs	gcKeepOutputs	bool	false	gc-keep-outputs

If true, the garbage collector will keep the outputs of non-garbage derivations. If false (default), outputs will be deleted unless they are GC roots themselves (or reachable from other roots).

In general, outputs must be registered as roots separately. However, even if the output of a derivation is registered as a root, the collector will still delete store paths that are used only at build time (e.g., the C compiler, or source tarballs downloaded from the network). To prevent it from doing so, set this option to true.