The fast-paced improvements in mortality in high-income countries since the early 1900s have led to a sustained increase in life expectancy. However, whether this linear trend will continue or life expectancy gains will decelerate in the near future remains unclear. To answer this question, we apply multiple established and recently developed mortality forecasting methods to estimate cohort life expectancy for individuals born between 1939 and 2000 in 23 high-income countries. Across all forecasting methods, our results robustly and consistently indicate a deceleration in cohort life expectancy. The previously observed pace of improvement, 0.46 y per cohort, declines by 37% to 52%, depending on the method used. Robustness checks suggest that these findings are unlikely to be solely due to downward bias in cohort life expectancy forecasts. Furthermore, an age-decomposition analysis indicates that this deceleration is primarily driven by a slower pace of mortality improvement at very young ages. Over half of the total deceleration is attributable to mortality trends under age 5, while more than two-thirds is explained by mortality trends under age 20. This pattern had already emerged in the observed data for the cohorts included in our analysis. Thus, even if these estimates turned out to be overly pessimistic, it is unlikely that the deceleration will reverse in the near future.