Summary: The primary solidification mode of austenitic stainless steel weld metals strongly dictates solidification cracking susceptibility. Provided that primary solidification mode selection is highly dependent on chemical composition, predictive tools such as the WRC-1992 diagram are often used to assess risk and/or design around potential solidification cracking concerns. In recent years, solidification simulations are becoming more commonplace with the advent and ever-growing adoption of CALPHAD methodologies, providing an additional avenue to predict primary solidification mode in austenitic stainless steels.In this work, high-throughput computational thermodynamic calculations have been used to develop a diagram to predict primary solidification mode for austenitic stainless steel weld metals. By simulating the stable and metastable liquidus temperatures for randomly generated austenitic stainless steel chemistries, a new set of nickel and chromium equivalency relationships have been developed that provide a sharp delineation between primary austenite and primary ferrite solidification modes under equilibrium conditions. Comparisons between legacy experimental data and computational thermodynamic calculations suggest that undercooling at the solid-liquid interface promotes metastable primary austenite solidification in stainless steel chemistries that fall near the equilibrium austenite-ferrite transition during conventional arc welding solidification conditions. Multicomponent dendrite growth theory has also been applied to help rationalize the occurrence of metastable primary austenite solidification. Using this information, a correction scheme has been established to modify the new primary solidification mode diagram to account for dendrite growth kinetics. A series of controlled gas tungsten arc spot welds have been performed on various arc-cast alloy chemistries that fall near the austenite-ferrite transition to assist with validation of the new primary solidification mode diagram. Validation efforts highlight that the location of the metastable austenite-ferrite transition is sensitive to both alloy chemistry and solidification conditions. An overview of the computational thermodynamic simulation framework, diagram construction, and experimental validation will be provided.While the new primary solidification mode diagram was constructed using a chemical composition range that covers many common austenitic stainless steel grades, the methodology developed here can be used to generate similar diagrams in the future and greatly reduce experimental burden. Examples where this methodology can be applied include cases where the chemical compositions and/or solidification conditions of interest differ from those explored here, or when increased resolution is needed within a narrow chemical composition range.