The actual API differences between Helios and seL4 are somewhat subtle, rather than a broader difference of design philosophy. For instance, the layout of the bootinfo structure is different - PML4/PDPT/PD/PT objects are stored in separate capability regions so that userspace can more reliably distinguish them without architecture-aware heuristics. Little things like that. And of course, the implementation is wildly different from seL4.

To be clear, I am specific about the "seL4" inspiration rather than the "L4". Naturally L4 plays a role, but Helios's API design has a pretty obvious influence from seL4 specifically.