Whatsapp backup which used to be free on google cloud storage will soon start coming with a subscription. Earlier when you backup your media and chats on WhatsApp, the storage limit does not count. As you can backup to Google cloud storage unlimitedly.
A few months back, WabetaInfo spotted an option to manage backups size on Whatsapp. This is unusual, as your backups don’t count against your Google cloud Storage.
For example, if 2GB was allocated as free storage, and you have 4Gb of data to backup, 2GB will be Backed up and the remaining 2GB will count against your storage.
Last year, Google removed photo backups from Google photos requiring users to subscribe to unlimited storage to back up their files. So, from speculations; WhatsApp might ask you to pay for a subscription to access more storage for backups.