Welcome S4HANA on-premise 1809! We already have an On-Premise version of 2018.
After 1511, 1610, 1709 is the turn of 1809.
All the details you can check on these official SAP links
2625407 – SAP S/4HANA 1809: Release Information Note
https://launchpad.support.sap.com/#/notes/2625407
SAP on-premise:
https://help.sap.com/viewer/product/SAP_S4HANA_ON-PREMISE/
What’s New Viewer – SAP S/4HANA 1809:
SAP recently announced the latest release of its SAP S/4HANA Cloud, thus delivering a variety of new scenarios, powered by artificial intelligence, that further drive the intelligent enterprise. It must also be noted that the updates of the 1808 release of SAP S/4HANA Cloud are now available for the manufacturing as well as professional services industries.