Now we have established north south connectivity. Its time we make provision for east west communication.
Based on design decisions and customer requirements you can connect overlay segments to Tier-0 Gateway or Tier-1 gateway. Both will work and machines connected to segments will be able to communicate.
But to keep up with the ever changing needs of technology and customers, its a good choice to go with Tier-1 gateway for your east-west communication. Not just that it has many other use cases.