Caveat emptor, I don't write Zig but followed its development closely for awhile. A core design element of zig is that you shouldn't be stuck with one particular memory model. Zig encourages passing an allocator context around, where those allocators conform to a standardized interface. That means you could pass in different allocators with different performance characteristics at runtime.

But yes, there is a default allocator, std.heap.page_allocator