Linked list stack has O(n) space complexity because: 1) Each element requires a node with data and reference, 2) Space grows linearly with number of elements, 3) Additional overhead for node pointers, 4) No unused space unlike array implementation, 5) Memory allocated dynamically as needed, 6) No preallocation required, 7) Space efficiency depends on element size and pointer overhead, 8) Typical trade-off for dynamic data structures.