Thanks. I just found this too, which seems to confirm that the "without a carrier" has the bands for all the major networks:
The SIM-Free iPhones option are unlocked and compatible with all four major networks in the US including AT&T, Verizon, T-Mobile and Sprint. The SIM-Free iPhone is only available from apple.com or your local Apple retail store.
The SIM-Free iPhone 8 and iPhone 8 Plus are also compatible with numerous prepaid wireless networks including but not limited to Straight Talk, Net 10 Wireless, Total Wireless, Tracfone, Cricket, MetroPCS, Simple Mobile, AT&T Prepaid, Verizon Prepaid, and others.
The SIM-Free iPhone 8 and iPhone 8 Plus are compatible with both the CDMA network technologies used by Verizon and Sprint as well as the LTE technology used by AT&T, Verizon, T-Mobile and Sprint.
The SIM-free iPhone 8 is model A1863 and the SIM-free iPhone 8 Plus is model A1864. The SIM-free iPhone models are the same iPhones that they sell to Sprint and Verizon customers. AT&T and T-Mobile customers recevieve the iPhone 8 Model A1905 and iPhone 8 Plus model A1897. These models are identical to the other models except they do not support the CDMA network technologies uses by Verizon and Sprint.