In a nutshell: Starting March 2024, Google is allowing individual users to change their account username. The old email remains as an alternative and uses the same inbox. App developers should check whether their systems support this change.
From March 31 onwards, US users can change their Google account username without losing their account, inbox or data. This update also affects apps that rely on Google sign-in or email-based user identification.
Many people still use old email addresses that no longer match their identity – whether due to a name change, a career shift, or simply because the old username is no longer appealing. This update solves the issue in a new way: when a user changes their username, the original email address remains linked to the account as an alternative address. Both email addresses lead to the identical inbox. Sign-in and email sending work with both addresses. This feature was previously only available to Google Workspace business users and is now also available for private Google accounts with @gmail addresses. App developers should review how their integrations with Google sign-in or email-based user identification are affected by this change.