The authors report a significant improvement in the systematic uncertainty of an optical lattice clock, achieving a total uncertainty of \(8.1 \times 10^{-19}\) in fractional frequency units. This represents the lowest uncertainty recorded for any clock to date. The clock uses a dilute ensemble of fermionic strontium atoms trapped in a vertically-oriented, shallow, one-dimensional optical lattice. Key advancements include precise control of collisional shifts and the lattice light shift, as well as a revised blackbody radiation (BBR) shift correction by evaluating the \(5s4d^{3}D_{1}\) lifetime. The second-order Zeeman coefficient for the least magnetically sensitive clock transition is also measured, with all other systematic effects having uncertainties below \(1 \times 10^{-19}\). The BBR shift is the most significant source of uncertainty, and future cryogenic operation is expected to reduce this uncertainty to the low \(10^{-19}\) level.The authors report a significant improvement in the systematic uncertainty of an optical lattice clock, achieving a total uncertainty of \(8.1 \times 10^{-19}\) in fractional frequency units. This represents the lowest uncertainty recorded for any clock to date. The clock uses a dilute ensemble of fermionic strontium atoms trapped in a vertically-oriented, shallow, one-dimensional optical lattice. Key advancements include precise control of collisional shifts and the lattice light shift, as well as a revised blackbody radiation (BBR) shift correction by evaluating the \(5s4d^{3}D_{1}\) lifetime. The second-order Zeeman coefficient for the least magnetically sensitive clock transition is also measured, with all other systematic effects having uncertainties below \(1 \times 10^{-19}\). The BBR shift is the most significant source of uncertainty, and future cryogenic operation is expected to reduce this uncertainty to the low \(10^{-19}\) level.