
First Vivaldi 1.6 snapshot based on Chromium 55 has been released and available for download for windows, Mac and Linux Platforms. The snapshot 1.6.682.3 offers the option to name tab stacks, the feature is still work in progress and hence disabled by default. This snapshot improves reader mode and comes with a fix to mouse cursor displaying in the full screen video issue.
Enable Tab stack renaming in Vivaldi 1.6
1. Click v icon, Tools > Settings > Tabs > Tab Settings > Tab Features, check Allow Tab Stack Renaming

After that, group two or three tabs and right click on a tab stack, and choose Rename Tab Stack.
Tip: You can stack tabs of same domain by choosing ‘Stack tabs by Host’ option on the context menu.
READ: Vivaldi 1.5 with Easier Tab Selection by domain
You can download Vivaldi 1.6.682.3 snapshot from here.