The new iPhone 17, iPhone 17 Pro, and iPhone 17 Pro Max continue to offer mmWave 5G connectivity in the United States, but the faster 5G speeds have not yet expanded to other countries. Outside of the U.S., the new iPhone models are limited to sub-6GHz 5G.
mmWave 5G has been exclusive to the United States since 5G connectivity launched in the iPhone 12. Other countries have been slower to adopt mmWave 5G, but it is becoming more widely available in countries like Australia, China, South Korea, Japan, and Europe. The higher frequency mmWave spectrum is not as practical as lower and mid-band 5G spectrum because of its limited range.
It's expensive for carriers to build mmWave networks, and it is expensive for Apple to offer the hardware to connect to those networks. Carriers don't have motivation for faster 5G when devices don't support it, and Apple doesn't see the need to roll out mmWave support in countries where adoption is low.
mmWave offers the fastest 5G speeds, but it primarily makes sense for big cities and crowded locations like concert venues, stadiums, and airports. It is short range, and cannot penetrate obstacles like sub-6GHz 5G can. Sub-6GHz is more widely adopted because it works in cities, suburban areas, and rural locations.
Unless something changes with 5G adoption and rollout, it's not likely that Apple's stance on mmWave 5G availability is going to change. In fact, the M4 iPad Pro models eliminated mmWave 5G support entirely, and Apple opted for 5G modems that only support sub-6GHz spectrum.
Because the iPhone Air has Apple's custom-designed C1X modem, it also does not support mmWave 5G. Like the C1, the C1X is only compatible with sub-6GHz 5G. The other iPhone 17 models use Qualcomm modems and in the U.S., can use mmWave spectrum on networks that offer it.
