The Librem 13 was long talked about having Coreboot over a proprietary BIOS while the initial models still had shipped with the conventional BIOS. Finally in 2017, they have now Coreboot at what they consider to be 100% complete for this Linux-friendly laptop.
The remaining issues -- including instability with M.2 SATA, a headphone jack issue, and other bugs -- have now been addressed. But still unresolved is the situation around the Intel Management Engine (ME) blob.
The changes for Librem 13 support in Coreboot have all been upstreamed to their Git repository. Aside from Intel's ME still being investigated, the situation isn't entirely resolved for Librem 13 v1 owners as Purism is still investigating the best ways to redistribute their new Coreboot image and to make it easy for their customers to replace their BIOS with this new Coreboot implementation.
More details on their Coreboot progress via this puri.sm blog post.