The study of nuclear beta decay has been at the forefront of our current understanding of the physical landscape, 

and continues to play an essential role in the search for beyond Standard Model physics. In order to separate the 

wheat from the chaff of the myriad possible theoretical extensions, a reliable estimate of the Standard Model 

contribution is indispensable. Recently, the description of the allowed beta spectrum shape was revisited and 

extended in order to tackle these challenges. Besides the study of the fundamental nature of the weak interaction, 

the beta spectrum shape is an essential ingredient in several outstanding problems in particle physics, such as 

the reactor antineutrino anomaly. We will provide an overview of the current state-of-the-art and its challenges, 

and discuss its implications on the reactor anomaly.