Expected number of z ~ 10 candidates in the different fields assuming the LF to be as measured at z ~ 8 (top; Bouwens et al. 2011b) or as expected from extrapolating the z ~ 4–8 trends to z ~ 10 (bottom). The one detected source is in stark contrast to the ~27 sources expected if the LF was constant across 170 Myr from z ~ 10 to z ~ 8. The LF appears to evolve at a significantly accelerated pace with respect to the empirical evolution observed across z ~ 4–8. Six sources at z ~ 10 should be detected when extrapolating the lower redshift trends, while only one probable candidate is found.