Sprint software update support page for Nexus 5 has now being updated and posted out that there is a new update coming within this week. Sprint had to addressed that the new 4.4.3 software dubbed as build version KTU84F will be hitting Nexus 5 beginning April 14, 2014. The said KTU84F 4.4.3 update brings the Sprint Spark band 26 and band 41, and some other Sprint default stuff might also as well gets new tweaks.
The KTU84F 4.4.3 is expected to come as of the release date schedule, but it seems the rolling out has not started yet. So maybe this update can be seen sooner, so just stick around and just set or allow your Nexus 5 to received the OTA update notification SMS automatically.