Apparently, in the Pixel 4 will be support Dual SIM Dual scheme is Active.
On the portal, which publishes the source code of Android, there was the edit, which States that 2019 will be Pixel dual SIM card.
In this case, since we are talking about the software, this refers to the number of simultaneous SIM.
Models Pixel 2 and Pixel 3 are like ordinary slots for SIM-cards and virtual card eSIM. However, users can’t use a physical SIM card and eSIM. This means that Pixel 2 and Pixel 3 support Dual SIM scheme Single Standby (DSSS). Although you can have two SIM cards for two different networks, you will not be able to receive calls or text messages on the inactive SIM card slot.
Apparently, in the Pixel 4 will support Dual SIM scheme Dual Active (DSDA) with the possibility of simultaneous operation of two slots, as is done in many Chinese phones.
This step is quite understandable for the company Google, which is trying to increase its presence in the markets of Europe, Middle East and Africa. In the US, where smartphones often are sold with a contract of one of the major mobile operators, two SIM cards are not too popular.
Add Google rumored to be planning to release in the first half of lightweight versions Pixel 3 Pixel 3 Lite and Lite XL, which will provide most of the features of more expensive models in the family Pixel, but in a more affordable price range. It should also help to gain a foothold in new markets.