• Service Accounts and OAuth 2.0 tokens are now used for data migration authorization. This replaces the deprecated OAuth 1.0 protocol.
• GAMME now uses the Gmail API for mail migration and label creation, replacing the Email Migration API v2 and Email Settings API, respectively.
• Reserved labels are now prefixed with an underscore to ensure proper nesting in the Gmail web interface. For example, a folder named "Inbox/Receipts" is migrated as "_Inbox/Receipts."
• If the migration user list includes a user that doesn't exist or there's an authorization issue, GAMME now detects the problem in all cases and doesn't try to migrate that user. Previously, GAMME would try each message individually and the failure would take a longer time.
• Minor UI and logging improvements.

• Multiple labels with names more than 225 characters long could cause a crash. 
• Messages in subfolders of Deleted Items were not being correctly marked as Trash in Gmail.
• Messages migrated from Exchange Public Folders to Google Groups show sender as "[email protected]."
• GAMME would crash if any command line flag or setting content included "%s."
• GAMME would fail to migrate the sender SMTP address in some rare cases.
• IMAP commands and responses in the logs were sometimes truncated.

Source: Google Apps update alerts