The Square Kilometre Array is a global research infrastructure project to construct and operate a radio telescope observatory of unprecedented scale. The first stage of the project’s implementation (SKA1) has concluded its design phase and is about to begin construction in 2021. Composed of two interferometric arrays covering a frequency range of 50-350 MHz in Australia (SKA-LOW) and 350 MHz to 15.4 GHz in South Africa (SKA-MID), the observatory provides sensitivity and resolution which advance the currently available research infrastructure capabilities across a range of scientific frontiers. We describe the design development process for the SKA1, the antenna design and specifications, and the current construction planning and schedule.