Earlier this week a minor update was released for Vivaldi. A new update mechanism was used (for the first time) to distribute this version to existing Vivaldi clients; according to the release notes for version 1.5.658.56, this reduced the size of the download to 323 kilobytes. The full download for Vivaldi 1.5.658.56 is 38.5 megabytes.
The update itself includes a few minor bug fixes, none related to security.