As reported earlier, Brock Lesnar came to an agreement on a new contract with WWE before last week’s RAW. The deal is described as short-term in nature and the only confirmed appearance of Brock Lesnar being at the WWE’s Greatest Royal Rumble event. It is a possibility that Lesnar would only work this one match under the contract even though the contract is not listed as a one-match deal, with the likelihood of the contract expiring as early as August, even before WWE SummerSlam.
The reason the length of the contract was not known is because then it would basically reveal the date when Lesnar would lose his Universal Championship.
The deal also allows Lesnar to negotiate for a UFC fight while under contract with WWE. This only allows for him to negotiate however, as the fight itself will have to take place when the contract expires.
The contract is said to be negotiated by Brock Lesnar and Vince McMahon directly, unlike most contracts which are handled by Triple H and Talent Relations department.
Source: Wrestling Observer Newsletter