Transfer set of repositories from one gitlab group to another subgroup all at once

The repositories/projects themselves still need to be exported by API, one by one.

But the new "Group Import/Export " feature from GitLab 13.0 (May 2020) can be a welcome addition.

Export and Import Groups in the UI

Previously, users could only migrate groups by using the Export/Import API to create an Export file, then using the API a second time to upload the file to the target instance.

As a first step toward a more frictionless solution, we have enabled Group Export in the GitLab UI.
We plan to introduce similar Import functionality to the UI within the next few weeks.

See documentation, issue and Epic.

See GitLab 14.2 (August 2021)

Group Migration achieves parity with group import/export

The new GitLab Migration feature can now migrate an entire group with all its subgroups and related data. The data migrated includes everything contained in group exports, making this a much easier way to migrate entire groups.
The pre-existing group import/export is a two-step process that requires exporting a file and then importing it into another GitLab instance.

Now, users can initiate a group migration with a single click. Migration also includes all the subgroups and their data, which previously required separate export and import processes for each subgroup.

See Documentation and Epic.