ImportanceFour clinical phenotypes of sepsis based on data from electronic health records have been proposed. Although promising, the generalizability of these phenotypes remains uncertain, and multisite validation is needed.ObjectiveTo validate, using the same methods and inclusion criteria, the 4 clinical phenotypes derived from Sepsis Endotyping in Emergency Care (SENECA) data.Design, setting, and participantsThis multisite retrospective cohort study uses data on adult patients admitted to the emergency departments in Stockholm, Sweden (January 1, 2011, to September 1, 2023); Oxford, England (February 4, 2014, to June 20, 2021); and Oslo, Norway (January 4, 2019, to October 9, 2023) university hospitals. Included encounters are those with body fluid cultures taken, documented antibiotic administration, and Sequential Organ Failure Assessment scores of 2 or more, all within 6 hours of admission. Data analysis was conducted from November 2, 2023, to September 1, 2025.Main outcomes and measuresConsensus clustering with k-means was used to derive 4 clinical phenotypes at each site, comparing them with the SENECA-derived phenotypes, as well as with one another.ResultsThere were 30 865 patient encounters in Stockholm (mean [SD] age, 68 [16] years; 18 165 men [59%]), 15 575 in Oxford (mean [SD] age, 71 [18] years; 9067 men [58%]), and 1806 in Oslo (mean [SD] age, 71 [17] years; 1068 men [59%]). There was little consistency between the SENECA clinical phenotypes and each site's own phenotypes, with a Cohen κ of 0.32 for Stockholm, 0.37 for Oslo, and 0.40 for Oxford; the Adjusted Rand Indices were 0.21 for Stockholm, 0.27 for Oslo, and 0.26 for Oxford. There was also little consistency between the phenotypes derived in Stockholm, Oxford, and Oslo.Conclusions and relevanceThis study suggests that the 4 clinical phenotypes of the SENECA data are not generalizable across 3 independent cohorts. This calls for further exploration of possible underlying sepsis subgroups using alternative approaches that mitigate the inherent stochasticity in many unsupervised and semisupervised clustering methods.