This paper describes the GISS‐E2.1 contribution to the Coupled Model Intercomparison Project, Phase 6 (CMIP6). This model version differs from the predecessor model (GISS‐E2) chiefly due to parameterization improvements to the atmospheric and ocean model components, while keeping atmospheric resolution the same. Model skill when compared to modern era climatologies is significantly higher than in previous versions. Additionally, updates in forcings have a material impact on the results. In particular, there have been specific improvements in representations of modes of variability (such as the Madden‐Julian Oscillation and other modes in the Pacific) and significant improvements in the simulation of the climate of the Southern Oceans, including sea ice. The effective climate sensitivity to 2 × CO2 is slightly higher than previously at 2.7–3.1°C (depending on version) and is a result of lower CO2 radiative forcing and stronger positive feedbacks.

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• Tropospheric warming and ocean heat uptake by 2014 are smaller in GISS-E2.1 and closer to observed trends than in its CMIP5 predecessor. • GISS-E2.1 climate sensitivity is higher than in CMIP5 GISS-E2 but forcing by greenhouse gases is smaller. • Atmospheric trends vary among model configurations with the storage of heat beneath the thermocline.