A steady source of Samsung information, Dutch gadget blog Mobiel Kopen, found the Galaxy S9 and the Galaxy S9+ in the database of the Chinese MIIT (Ministry of Industry and Information Technology) and on the website of FCCID.
These devices carry the model numbers SM-G9600, SM-G9608 and SM-G9650. The SM-G9600 is the Chinese version of the Galaxy S9, the SM-G9608 is the Taiwan version and the SM-G9650 the Chinese version of the larger S9 +. At the moment it is still unclear whether Samsung provides Dual SIM support for all S9 and S9+ models. It could vary per country.
These three models can be found in the database with the note / DS which indicates that they are dual-sim devices. With this it is confirmed that the Samsung Galaxy S9 and S9 + also in dual-sim version will be for sale.
According to previous report the Galaxy S9 could very well feature Dual SIM Dual VoLTE technology, as the Qualcomm Snapdragon X20 LTE modem will be available from the beginning of 2018. The predecessor of this modem, the X16 is used by the Snapdragon 835 processor. The newly released Snapdragon 845 integrates the X20 modem.