Two Nature Biotechnology reports delivered complementary methods to measure lipid nanoparticle (LNP) performance inside animals, providing quantitative readouts of endosomal escape—a bottleneck for RNA delivery. One study deployed a lysosomal barcoding strategy to quantify nucleic-acid escape into the cytosol across branched ionizable lipid chemistries; the other validated an in vivo assay to map endosomal escape kinetics and correlate them with hepatic delivery. Both papers provide experimental frameworks to compare LNP formulations directly in animals, enabling more predictive selection of leads for therapeutic programs. Developers of mRNA vaccines and gene-editing medicines now have standardized in vivo metrics to optimize ionizable lipids, helper lipids and formulations for liver and possibly extrahepatic targets.