Exemplars U5M Interview Guide: This is an example of the semi-structured interview guide used for key informant interviews described in the article, "Development and application of a hybrid implementation research framework to understand success in reducing under-5 mortality in Rwanda."

Extended data (supplemental) tables and figures: These are the supplemental tables and figures to accompany the article, "Development and application of a hybrid implementation research framework to understand success in reducing under-5 mortality in Rwanda."

Completed StaRI checklist: This is the Standards for Reporting Implementation Studies – StaRI – checklist completed for the article, "Development and application of a hybrid implementation research framework to understand success in reducing under-5 mortality in Rwanda."

Completed COREQ checklist: This is the COnsolidated criteria for REporting Qualitative research - COREQ - checklist completed for the article, "Development and application of a hybrid implementation research framework to understand success in reducing under-5 mortality in Rwanda."

Exemplars U5M Interview Guide: Interviews were conducted using a semi-structured guide, based on the IR framework, designed to understand EBI selection; the implementation process, from exploration to preparation, implementation, and sustainment; and contextual factors contributing to successes and challenges in each stage. The interviews also helped identify additional data sources important in understanding implementation and related outcomes.

Extended data (supplemental) tables and figures: Not applicable

Completed StaRI checklist for this article: Not applicable

Completed COREQ checklist for this article: Not applicable