Cumulative distribution function (CDF) of the modeled LGRB progenitors’ metallicities for redshifts z < 2.5, in blue. The CDF of the observed SHOALS LGRB host galaxy metallicities for z < 2.5 (Graham et al. 2019) are indicated in orange. The light orange shaded area shows the uncertainty in the observed CDF due to systematic offsets in the measurement of log₁₀(O/H), depending on the calibrations used, and the stellar mass of the galaxy which can be as high as Δ[log₁₀(O/H)] ≈ 0.7 dex (Kewley & Ellison 2008). As a reference, we indicate with a vertical dashed black line the median metallicity from the IllustrisTNG simulation at redshift z = 2, and lighter gray shaded areas delineate larger CIs of 68%, 95%, and 99% for the assumed star formation metallicity distribution.