Summary
If the mean time after [1] of the last 11 blocks (MTP-11) is greater than or equal to the UNIX timestamp 1605441600 (November 15, 2020, 12:00 PM UTC), Bitcoin Cash will upgrade the network consensus through rules according to this Specification. These changes to the consensus rules will take effect from the next block:
Bitcoin Cash's Difficulty Adjustment Algorithm (DAA) is being replaced with a new system called aserti3-2d.
Adding a new Coinbase rule.
The following changes are not consensus changes but are recommended as policy changes for Bitcoin Cash implementations:
Automatic playback protection for future upgrades.
Algorithm to adjust the difficulty
Bitcoin Cash's Difficulty Adjustment Algorithm (DAA) is being replaced with a new algorithm called ASERT.
The specific implementation is called aserti3-2d. See full specification for details: ASERT.
Coinbase rule
The new Coinbase rule is intended to finance development projects that work on a common Bitcoin Cash infrastructure.
The Coinbase rule enforces that at least 8% of the block reward must be given as a single expense to the following Bitcoin Cash address: bitcoincash: pqnqv9lt7e5vjyp0w88zf2af0l92l8rxdgnlxww9j9.
The amount of expense must be equal to or greater than the required integer, which is calculated using integer math as follows:
required = (8 * blockReward) / 100
Automatic repeat protection
The purpose of automatic replay protection is to act as a mechanism to expire the full node version. It is intended that full validation nodes that are not upgraded will automatically disconnect from the main network after the next upgrade on May 15, 2021. Nodes implementing the next upgrade will remove this automatic replay protection so that all regular wallets can continue using the default ForkID without change to follow the updated main chain.
If the mean time after [1] of the last 11 blocks (MTP-11) is less than the UNIX timestamp 1621080000 (upgrade from May 2021), Bitcoin Cash full nodes MUST enforce the following rule:
Fork [2] must be 0.
If the mean time after [1] of the last 11 blocks (MTP-11) is greater than or equal to UNIX timestamp 1621080000 (May 2021 upgrade), Bitcoin Cash full nodes implementing the November 2020 consensus rules should make the following change force:
Update forkid [2] to 0xFFXXXX, where XXXX is any hex value. ForkIDs that start with 0xFF are reserved for future protocol updates.
This special consensus rule must NOT be implemented by the Bitcoin Cash Wallet software. Wallets that follow the upgrade shouldn't need to change anything.
References
[1] Median Time Past is described in the bitcoin.it Wiki. It is guaranteed by consensus rules that they will increase monotonically.
[2] The ForkId is defined according to the repetition-protected Sighash specification.