After rolling out voice calling to the public channel last month, WhatsApp Beta has received an update that allows you to toggle low data usage for voice calls placed using the messaging app. The ability to conserve data comes at the cost of call quality, as enabling the setting lowers the quality of the call.
From the screenshots provided to us, it looks like the chat and call options are getting consolidated, with the "low data usage" toggle located in the "chats and calls" section. The changes should be making their way to the public WhatsApp app in the coming weeks.
Thanks for the tip and screenshots Abhishek!