So are they all recompiled? What about compilation/linking time? Or is this not a concern since the zig compiler is fast?

Zig sources go into a single big compilation unit. C sources can be split into multiple CUs and Zig has a neat caching system that integrates with clang to only rebuild a CU when necessary (you don't have to do anything to set it up).

An incremental compilation feature is coming to the self-hosted compiler: https://kristoff.it/blog/zig-new-relationship-llvm/

C source files are only compiled on full rebuilds, or when the C source file changes, just like in regular C projects. You can distribute precompiled libraries, but I think given that one of Zigs prominent features is simple cross-compilation to all sorts of platforms, compiling from source is preferred.

The @import method is only for "importing" C headers with declarations and have them automatically converted to Zig interface declarations (so in most cases you don't need manually maintained language bindings). For compiling the associated C soure files, Zig has a builtin C compiler.

I think you misunderstood my question. I am not (in this question) interested in C or C interopability of zig, but how to structure larger zig project (how zig thinks this should be handled)

Yeah, I realized that after I hit send :)

For regular Zig source files, you just import them into other Zig source files, up to the "main file". Such imports are wrapped into a module struct (imported modules are just regular structs). The Zig build system takes care of efficiently compiling all this with proper incremental build support (one can explore the zig-cache subdirectory which is maintained by the zig compiler for details).

For example, these are the imports in a top-level file:

https://github.com/floooh/pacman.zig/blob/ed42fad79c3e9b4432...

The sokol.zig file groups other modules under a common namespace:

https://github.com/floooh/pacman.zig/blob/main/src/sokol/sok...

...which in turn imports "leaf modules" like this:

https://github.com/floooh/pacman.zig/blob/main/src/sokol/aud...

...it's one of the most straightforward module systems I've seen yet in any language.

Just like JavaScript modules, kind of.