Based on what I’ve seen so far, Librem 5 will support Sprint in the US and CDMA. Twigby says if those two things are true about the phone, it will likely work with their service.
I just want to confirm that Librem 5 will support CDMA and Sprint in the US. Yes, no?
Sprint uses CDMA BC1 (1900 PCS) and CDMA BC10 (Secondary 800 MHz), which are not supported by any of the 4 available modem models.
Sprint uses LTE B25, B26 and B41, so your best option is the BM818-A1 modem which supports LTE B25 and B26, but you won’t get any CDMA coverage (unless you buy your own modem and install it in the Librem 5).
The general rule with Sprint is if Sprint doesn’t sell it, they won’t allow it on their network. The current BYOD list at https://community.sprint.com/t5/Device-Solutions/ANSWER-Is-My-Phone-Eligible-for-BYOD-with-Sprint/ta-p/1020211 is basically various iPhones, Pixels, Motos, and Galaxies (unlocked variants of phones they already sell). If Purism paid Sprint to have the Librem 5 certified for use on their network then it could happen, but outside of that the chances that Sprint will let the Librem 5 onto their network are practically zero.