For quite some time music has been mastered at 24/96, then 24/192kHz.
Older analogue recordings were mastered at 16/44.1 during the CD generation and later at 24/96. These hires masters were down converted for CD distribution.
When remastering older recordings they are upsampled and become new "hires" masters. They can then be distributed as hires files (streaming, downloads) or converted back down for Redbook.
So all remasters exist as hires masters today.
But there are still many original digital masters that are streaming at 16/44.1. However, they're being replaced with upsampled remasters.
Older analogue recordings were mastered at 16/44.1 during the CD generation and later at 24/96. These hires masters were down converted for CD distribution.
When remastering older recordings they are upsampled and become new "hires" masters. They can then be distributed as hires files (streaming, downloads) or converted back down for Redbook.
So all remasters exist as hires masters today.
But there are still many original digital masters that are streaming at 16/44.1. However, they're being replaced with upsampled remasters.