Bitcoin Core writes:
CSV softfork – Important upgrade instructions for miners
There is an ongoing soft fork of the Bitcoin consensus rules. While everything appears to be proceeding well, this article contains important information and checklists for miners and pool operators which must not be ignored.
If there is any doubt, miners and pool operators are welcome to contact us.
Check all your nodes have been upgraded to Bitcoin Core 0.12.1 or compatible software. This must happen before block #419328. Note that if your GBT client(s) implement the protocol correctly, you will need to patch in PR #8176 (patch) or use Bitcoin Knots which already includes it.
If you hardcode the block version please unset bit 0 of the version field before block 419328, or preferably stop hardcoding it and let bitcoind do it automatically.
Use a nLockTime value of 0xffffffff for the generation transaction to avoid any potential conflict with BIP113.
If you have to use a different nLockTime value, you must follow the instructions carefully.
Status of CSV soft fork
The “CSV” soft fork has reached the “locked in” threshold required to proceed to activation. Out of the 2016 blocks from #415296 to #417311, 1946 (96.53%) signaled the readiness for the BIP68, BIP112 and BIP113 (“CSV”) softfork. As of block #417312 (2016-06-21 05:18:58 UTC), the CSV softfork is now in a “locked in” grace period for about 2 weeks up to block 419327. After that, the new BIP68, BIP112 and BIP113 rules will be activated and enforced by the network. It has passed the “point-of-no-return” and is irreversible without a massive rollback of the blockchain.
For all miners
During the grace period, all miners must upgrade to Bitcoin Core 0.12.1 or any implementation which supports the CSV softfork. In practice, at the time of writing, Bitcoin Core and Knots 0.12.1 are the only versions that supports the CSV softfork. Miners must double check to make sure all the mining nodes and backup nodes have been upgraded. Failing to do so may result in generation of invalid blocks, or cause your nodes to build upon any invalid blocks causing chain forks and monetary loss to the concerned miners and general Bitcoin users.
For miners who manually hardcoded the block version
By default, Bitcoin Core automatically set and unsets version bits as required, however, we are aware some miners hardcode the block version numbers. We strongly advise against hardcoding the block version because it can introduce risk to the Bitcoin system because the version signals support for certain consensus rules.
If a miner inadvertently has any nodes that don’t support the rules indicated by the block version, it could cause invalid blocks to be produced, and it could cause the miner to follow and build upon an invalid chain. In short, by not using the default value provided by bitcoind, it increases the risk of decoupling of block rules signalling and block rules enforcement.
Unlike the IsSuperMajority softfork used in BIP33/66/65, in the BIP9 softfork system, no blocks will be orphaned due to a wrong version number (as long as the version is >= 4, which is required by BIP65). Therefore, there should be no incentive for miners to hardcode the block version, which would unnecessarily increase the burden of maintenance and risks of human error.
However, if you are manually setting the block version against this recommendation, you MUST take specific action. Now that the “point of no return” grace period has been reached for CSV, you must unset the CSV version bit, bit 0. This means if you were signalling 0x20000001 you should signal 0x20000000. This MUST be changed before block #419328 or you will trigger “unknown softfork” messages in the logs of all BIP9 compliant nodes. For more information please see the Version Bits FAQ.
Failing to follow this advice may trigger the upgrade warning system of all BIP9 compliant nodes on the network, which will be very disruptive.
For miners that allow bitcoind to set the block version automatically, no further action is required. Please note it will keep generating blocks with version 0x20000001 until block #419328 at which point is will automatically unset bit 0.
With regard to the nLockTime field of the generation transaction
This is uncommon, but miners using the nLockTime field must pay extra attention due to the activation of BIP113.
If a miner is interfering with the nLockTime of the generation transaction in any manner, they must make sure that the value, if interpreted as an UNIX timestamp (i.e. >= 500000000), must be smaller than the median timestamp value of the past 11 blocks, unless the nSequence of the generation transaction is exactly 0xffffffff.
If you do not use nLockTime field of the generation transaction, please use a value of 0.
Failing to follow the above instructions may result in generation of invalid blocks, causing a chain fork and monetary loss of the concerned miners and general Bitcoin users.