This has already been implemented, and I totally missed it. I'm sorry!
The title of the announcement was Improving secondary calendar management with dedicated owners.
The article mentions (parts of) the change as follows.
"When a new secondary calendar is created, the creator becomes the calendar owner. For existing secondary calendars, an owner will be automatically assigned based on the calendar’s permissions. The calendar will inherit the organizational policies from its owner. This provides fine-grained control for admins to define policies for each calendar, such as data regions or assured controls.
Additionally, we’re introducing the ability to transfer secondary calendar ownership to another user in the same organization, through Google Calendar settings (for end users) or the Admin console (for admins). This is especially helpful when a calendar owner changes teams or leaves the organization, to ensure the calendar remains associated with the appropriate owner."
What the announcment does not mention is that a secondary calendar now loses it's ability to live on as long as there is at least one person with the Manage Sharing permission. It is now intrinsically tied to the one and only dataOwner. This is documented in some of the support articles for secondary calendars, as a Note.
Create & share group Calendar
Delete or remove a user from your organisation
Cancel or transfer events or secondary calendars before deleting a user
"Note: As a result of changes being introduced in 2026, when a calendar owner is deleted, their secondary calendars and all contained events are also automatically deleted and any further transfers won’t be possible."
It is not mentioned in the default support article on creating (secondary) calendars.
Create a new calendar
You need to take control of all essential secondary calendars in your organisation!
Of course, informing all your users of this may be enough, and they will in an orderly fashion always make sure that all secondary calendars they have created, and which need to exist after they leave the organisation, are properly transfered to a new owner well in time for their retirement.
Nah, I don't believe that.
I used GAM to print a list of all secondary calendars to a Sheet, with some filtering.
gam config auto_batch_min 1 csv_output_row_drop_filter "dataOwner:regex:^$,calendarId:regex:classroom" redirect csv - multiprocess todrive all users print calendars noprimary noresources nosystem fields dataowner oneitemperrow
I removed all calendars that didn't have a value for dataOwner and those created by Classroom, as those are not affected by this change (ownership transfer of Classroom is a completerly separate headache!). Cleared out all irrelevant columns and ended up with these.
primaryEmail, calendarId, dataOwner
I inserted a formula in D1 that compared the column primaryEmail with dataOwner, and set a 1 for true and 2 for false, while ignoring empty rows (usually found at the bottom of your sheet).
=ARRAYFORMULA(IF(ROW(A:A)=1, "primaryIsOwner", IF(A:A<>"", IF(A:A=C:C, "1", "2"), )))
Then I could remove all rows with 2s. Ended up with 224 unique secondary calendars with a known dataOwner.
These are the people I need to inform, and which I can help with ownership transfer if necessary, either with GAM or by managing the individual calendars directly in Google Calendar as superadmin.
You may already have thought of this, and have an existing process for managing all important secondary calendars.
If not, today is a great time to start doing just that.
--
https://wheretofind.me/@NoSubstitute