The SEGWIT contract is a prediction futures contract. The futures contract is Binary, meaning it will either settle at 0 or 100.
The SEGWIT contract is a prediction future on whether or not BIP141 (more info), also known as Segregated Witness, will be activated on the longest Bitcoin chain by the expiry date (Dec 31, 2017, 12:00 UTC).
SEGWIT will settle at 100:
SEGWIT will settle at 0 if the above conditions are not met.
The above conditions may be amended with notice at any time.
An activation period spans one difficulty period (2016 blocks). 95% of the blocks mined during an activation period must signal acceptance of BIP141 for SegWit to be activated.
BitMEX’s BLOCKS binary is independent from this contract. Both, or neither, may settle positively before the expiration date.
Please see the Binary Series Guide for more details.