Seven cervical vertebrae is one of the most conserved traits in mammals. Whether the neck is a few centimetres long or over two metres, the count is almost always seven, with only sloths and manatees deviating. The giraffe achieves its reach by stretching each individual bone rather than adding more.
The consequence is a set of engineering problems solved elsewhere in the body. Blood must be driven several metres upward, so the giraffe's mean arterial pressure is roughly twice that of a typical large mammal, supported by a thick-walled heart and tight elastic vessel walls. Valves in the jugular veins and a network of fine vessels at the base of the brain buffer the pressure surge when the head is lowered to drink.
A further detail is often missed. The first thoracic vertebra of the giraffe is modified towards a cervical form, giving extra flexibility without changing the formal count, which is why some accounts loosely describe an eighth neck bone.