2

One element was added, and a few notable things have happened: the len field is increased to 4, which makes perfect sense because the seq now holds 4 elements

the reserved field increased from 3 to 6. This is because Nim doubles the storage size when doing a new allocation - this is more efficient when repeatedly adding data without having to resize the allocation for every add()

note that the address of the seq itself also changed! The reason for this is that the inital memory allocation for the seq data on the heap was not large enough to fit the new element, so Nim had to find a larger chunk of memory to hold the data. It is likely that the allocator already reserved the area directly behind the seq to something else, so it was not possible to grow this area. Instead, a new allocation somewhere else on the heap was made, the old data of the seq was copied from the old location to the new location, and the new element was added.