Authors - Vijak Sethaput, Supachate Innet Abstract - The rise of digital currencies—encompassing cryptocurrencies, stablecoins, tokenized deposits, and central bank digital currencies (CBDCs)—has outpaced frameworks for understanding their coexistence as financial infrastructure. This paper proposes the Digital Finance Infrastructure Framework (DFIF): a four-layer architecture—Settlement, Commercial, Retail, and Open— that maps five digital currency categories to complementary infrastructure tiers and explicitly links each tier to smart-systems enablers, sustainability dimensions, and security considerations. This paper makes four contributions: (1) a seven-dimensional comparative taxonomy of five digital currency categories; (2) the DFIF framework; (3) a four-dimensional interoperability model; and (4) a six-category systemic risk taxonomy with evidence-based smart-system mitigations. We situate the DFIF against four established frameworks (IMF Money Flower, BIS Singleness of Money, Carstens Digital Money Galaxy, Brunnermeier Digital Currency Areas) and validate it against deployment evidence, including BIS mBridge (reaches MVP stage and BIS exit), Project Agorá (seven central banks), MiCA full applicability, Nigeria's eNaira (
