Bitcoin Cash which is the coin that diverged from the main Bitcoin chain in August 2017 where it initially started with a 8MB max block size, is forking in May 2018 to increase the max block size to 32MB.
The scheduled upgrade is set for May 15, 2018 where one of the main Bitcoin Cash implementations Bitcoin ABC, headed up by lead developer Amaury Sechet, announced the upgrade a few months ago.
The scheduled activation time will be on May 15 but there is no specific block height for this upgrade. The upgrade to the consensus rules will change based on the “Median Time Past” (MTP) method. On Tuesday, May 15 at 12:00:00 UTC, 2018 when the MTP takes place with the most recent 11 blocks equal to or greater than 1,526,400,000, the very next block will activate the hard fork.
The new maximum block size will allow for a much higher throughput of Bitcoin transactions on the cash network, where the maximum allowed message size of the blockchain is 32MB, maxing out the total available.
Other notable changes in the hard fork upgrade are the reactivation of several Bitcoin script operation codes (op_codes). These include:
OP_CAT, OP_AND, OP_OR, OP_XOR, OP_DIV, OP_MOD, OP_SPLIT, OP_NUM2BIN, and OP_BIN2NUM. Finally, the OP_RETURN data carrier size increases to 220 bytes.
At this time, the Bitcoin Cash blockchain is averaging around .5MB transaction blocks, but has seen blocks as high as 8MB. The additional transaction space will allow for more transactions per second.