CSi12N3 is a bioorthogonally activatable ionizable lipid containing two cleavable silyl-ether-linked C12 tails and a dual-amine headgroup. Formulated as SiLNPs, it remains relatively silent before activation but undergoes Phe-BF3-triggered desilylation, nanoparticle destabilization, and accelerated cytosolic mRNA release. The reported formulation produced up to 44-fold higher mRNA expression than SM-102 LNPs in vitro, with an approximately 10-fold activation-to-silent ratio. In a B16-F10 melanoma model, CSi12N3-based SiLNPs delivering GDNT mRNA induced tumor-localized pyroptosis and inhibited tumor growth without detectable systemic toxicity in the reported study. CSi12N3 is therefore a promising preclinical research lipid for externally controlled, tumor-selective mRNA delivery.