In the age of Intel's 8th Gen Coffee Lake CPUs, not to mention AMD's Ryzen+ chips, it's probably unlikely that you'll be considering one of Intel's old Kaby Lake X processors for your next PC build. Still, just in case you are thinking about buying an Intel Core i7-7740X or Core i5-7640X, you should probably know that they're about to be discontinued starting in this merry month of May, according to a product change notification on its website.
The pair of Kaby Lake X processors only launched in June 2017, but Intel have clearly decided this slightly odd, high-end enthusiast family of Core X-series chips simply aren't worth the hassle. They were originally intended to provide an entry-point into Intel's High-End Desktop (HEDT) platform, as they were much, much cheaper than the Skylake-X CPUs that launched around the same time.
The problem, however, is that they didn't play very nicely with the rest of the HEDT brood. For starters, each of the Kaby Lake X CPUs only ever had support for two memory channels, so half of the DIMM slots on your typical HEDT motherboard were pretty much completely useless. Then Coffee Lake came along and the Core i7-8700K pretty much made both of them obsolete. Hooray product lines!
The Kaby Lake X chips won't disappear immediately, despite Intel stating that their ominous-sounding 'Product Discontinuance Program Support' starting on May 7. Retailers will in fact have until the end of November to order their last batch of Kaby Lake X processors, and the last shipment date is set for May 31 2019, so you may still see them kicking around for a while yet.
However, when Intel's own Core i7-8700K offers six cores rather than four, has a higher max turbo boost speed of 4.7GHz compared to 4.5GHz, comes with a larger 12MB SmartCache and only has a 95W thermal design power (TDP) as opposed to 112W - all for roughly the same amount of money as the Core i7-7740X, no less - there really is no conceivable reason why you should snap one up over its superior Coffee Lake successor before it disappears.
As that age-old adage goes, let's just put this one down to experience and, er... pretend it never happened.