Per CSMS #16-000181:
Starting today, March 10, 2016, shipments valued at $800 or less will be eligible for release under the same processes and with the same restrictions as currently apply for de minimis shipments of $200 or less.
CBP has the right to require a formal entry on any shipment where additional information, bonding or protection is required. In the case of low value shipments, it is important to note that this treatment can be denied if used for the purpose of avoiding compliance with any pertinent law or regulation. That is especially important where revenue, import safety or serious trade enforcement issues are present.