The S8 packs a Qualcomm Snapdragon 835 CPU that can use faster data rates on the 4G spectrum referred to as Gigabit LTE. Apple, though, uses its own CPU and a mix of modems from both Intel and Qualcomm (the pains of supply chain management and high demand. This is often called dual-sourcing).
And while Qualcomm's modems can reach those speeds, Intel's latest reportedly can't. If that ends up being the case, Apple may have to limit Qualcomm's modems so that all iPhone 8s are functionally identical. That would mean no Gigabit LTE for anyone on Apple's devices.
Carriers and vendors alike are expected to start calling out Gigabit LTE as an important feature, and Qualcomm expects as many as 10 phones to offer those speeds. It would be a huge loss for Apple to be the only premium phone without it.
Of course, there are other options. Apple could drop Intel and use Qualcomm exclusively. Or, as CNET points out, Apple continue to use both chips, but use Qualcomm chips in the United States where Gigabit LTE is developing.
Gigabit LTE's name is a bit of a misnomer. You won't be able to download anything at 1 gigabit per second. Instead, the name is based on a theoretical top speed that devices could achieve as the network develops. That means that a phone like the S8, which does have Gigabit LTE, could get even faster over the next several years.
Of course, Apple hasn't always been the first to new technology, and it may be perfectly happy sitting this one out and waiting for Gigabit LTE to mature before releasing a phone that supports it. We'll find out this fall, when Apple is rumored to announce its next iPhones.