Stainless steels such as grade 316 are commonly used in various hydrogen applications, and the hydrogen embrittlement (HE) resistance of these steels is well-established. However, the high degree of alloying, particularly nickel, required to achieve the stable austenitic microstructure drives their relatively high cost and is a potential barrier to future implementation of a broad hydrogen infrastructure. The objective of a program including the efforts reported here is to develop lower cost steel alloys with high performance, through novel microstructural design, for use in hydrogen refueling infrastructure such as storage, compressors, and dispensing components. We are employing manganese (Mn) substitutions for nickel to produce both fully austenitic and duplex austenite-ferrite microstructures and evaluating potential alloy and microstructure design alterations through thermomechanical processing to enhance the HE resistance of the designed high Mn alloys. HE sensitivity of the high Mn (20-30 wt pct) steels in comparison to commercial 316L austenitic and 255 duplex stainless steels was investigated by means of rising displacement testing of circumferentially notched tensile specimens during in situ electrochemical hydrogen charging. Both austenitic and duplex microstructures produced in high Mn alloys exhibited promising toughness in hydrogen results, as compared to the stainless steels.