Reionization history in ΛCDM based on new JWST observations of structure formation in the early Universe. Lower panel: the neutral fraction x_HI as a function of redshift z, for a cutoff M_UV = −14.6 and a JWST-calibrated ionizing efficiency, ξ_ion, and escape fraction (f_esc) inferred from low-z analogues. The blue data points represent measured observational constraints (see text for references). Upper panel: CMB optical depth, τ_CMB, as a function of z. The blue band represents the Planck measurement and its uncertainty (Planck Collaboration VI 2020). The ${\chi }_{\text{d}.\text{o}.\text{f}.}^2$ for the x_HI fit is 4.36, and τ_CMB differs from the Planck optimized value by ∼2σ. The new JWST galaxy observations thus create significant tension for the standard model, both for the reionization history and the CMB optical depth.