As you mentioned, the feature request is logged in our Feedback Portal here
. Currently, it is marked as Approved, which means it hasn't started development yet (you'll see the status change from "In Development" to "Completed" when it's done).
At this time, the document processing libraries do not surface such an API, so there is not a workaround that you can use to accomplish this.
If this is a mission critical requirement, you could try the conversion yourself:
1 - First, export (or save) as xlsx as you'd normally
2 - Get the saved xlsx file and manually convert it to xlsb (see here
for how to do this)
Then, in the future when we add the format, you can go back and optimize your code to so the single step export as xlsb.
Note: I cannot confirm the approach in that StackOverflow post will work as this is just a suggestion. You could research other xlsx -> xlsb conversions to achieve the same outcome.
I hope I was able point you in the right direction.
Lance | Tech Support Engineer, Sr.
Telerik by Progress
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