Meta will begin rolling out 'username' starting late June 2026

It is an optional feature that allows user to hide their phone numbers when messaging businesses

When user adopts an username, their phone number will no longer appear in webhook payloads, instead, a Business Scoped User ID (BSUID) is returned

What is BSUID

A BSUID is a unique Meta-generated identifier for a user-business pair that allow businesses to message users without their phone number, is valid within the same business portfolio and becomes invalid if the user changes their WhatsApp phone number

It should be stored for future communication when the user's phone number is unavailable

What is Parent BSUID

A parent BSUID is a Meta-generated identifier that represents a WhatsApp user across multiple business portfolios linked to the same Parent BSUID account, allowing any WhatsApp Business Account (WABA) phone number in those portfolio to message the user using the same identifier, unlike a regular BSUID which can only be used by a single business

It is recommended to store both the Parent BSUID and BSUID, using the Parent BSUID for messaging and BSUID as fallback if the portfolios are later unlinked

More information regarding the rollout of BSUID can be found here on Facebook Developer Guide