The paper discusses the reactor antineutrino anomaly, a deviation from the expected flux of electron antineutrinos observed in reactor experiments. The authors reevaluate the antineutrino spectra for various fissile isotopes, leading to a 3.5% increase in the flux. This increase, combined with previously reported small deficits at shorter distances, results in a larger average deficit of 5.7%, which they call the "reactor antineutrino anomaly." This anomaly is significant at the 98.6% confidence level and is consistent with being independent of the distance to the reactor core at distances greater than 15 meters. The authors analyze the impact of this new flux evaluation on past, present, and future reactor neutrino experiments. They find that the anomaly is consistent with the existence of a fourth non-standard neutrino state, driving neutrino oscillations at short distances. The required mass difference, \(|\Delta m_{\text{new}}^2|\), is significantly larger than those required by solar and atmospheric experiments, suggesting the presence of a fourth neutrino beyond the standard model. The paper also revisits the sensitivities of the CHOOZ and KamLAND experiments to the mixing angle \(\theta_{13}\) and combines the results to disfavor the no-oscillation hypothesis at 99.8% confidence level. The oscillation parameters are constrained to \(|\Delta m_{\text{new}}^2| > 1.5\) eV\(^2\) (95%) and \(\sin^2(2\theta_{\text{new}}) = 0.14 \pm 0.08\) (95%). The authors conclude by discussing experimental programs aimed at testing the anomaly further.The paper discusses the reactor antineutrino anomaly, a deviation from the expected flux of electron antineutrinos observed in reactor experiments. The authors reevaluate the antineutrino spectra for various fissile isotopes, leading to a 3.5% increase in the flux. This increase, combined with previously reported small deficits at shorter distances, results in a larger average deficit of 5.7%, which they call the "reactor antineutrino anomaly." This anomaly is significant at the 98.6% confidence level and is consistent with being independent of the distance to the reactor core at distances greater than 15 meters. The authors analyze the impact of this new flux evaluation on past, present, and future reactor neutrino experiments. They find that the anomaly is consistent with the existence of a fourth non-standard neutrino state, driving neutrino oscillations at short distances. The required mass difference, \(|\Delta m_{\text{new}}^2|\), is significantly larger than those required by solar and atmospheric experiments, suggesting the presence of a fourth neutrino beyond the standard model. The paper also revisits the sensitivities of the CHOOZ and KamLAND experiments to the mixing angle \(\theta_{13}\) and combines the results to disfavor the no-oscillation hypothesis at 99.8% confidence level. The oscillation parameters are constrained to \(|\Delta m_{\text{new}}^2| > 1.5\) eV\(^2\) (95%) and \(\sin^2(2\theta_{\text{new}}) = 0.14 \pm 0.08\) (95%). The authors conclude by discussing experimental programs aimed at testing the anomaly further.