Final Update: Microsoft have indeed confirmed today that this was simply a display error (which has since been corrected), and Xbox Live Gold is included as part of the benefits of the ‘Xbox Game Pass Ultimate’ membership.
A keen-eyed member of our staff caught that the description for Game Pass for Console on the Xbox Store is showing that Xbox Live is now included in the base tier of the service. After we tested it out the system did not allow us to access multiplayer titles that require Xbox Live Gold with only Xbox Game Pass for Console as of yet.
Previously Xbox Live Gold required either its own $10 subscription or it was part of the Game Pass Ultimate service. We have reached out to Microsoft for comment.