There is no generally accepted tensile strength that makes a grade into an ultra-high strength steel: some companies say 780 MPa, others say 980 MPa, 1180 MPa or 1270 MPa.
Previously, WorldAutoSteel, the association of steelmakers focused on AHSS for cars, proposed the following approximate definitions based on minimum tensile strengths (TS):
Advanced high-strength steels (AHSS) ≥ 550 MPa TS
Ultra-high strength steels (UHSS) ≥ 780 MPa TS
GigaPascal steels ≥ 1000 MPa or 1 GPa TS
However, WorldAutoSteel’s 2021 AHSS Application Guidelines puts the minimum tensile level for AHSS steels at 440 MPa, while acknowledging no agreed-upon level for UHSS steels. It could be that the less frequently used term “GigaPascal” will become more popular because there is no ambiguity regarding its definition: steels with tensile strengths of 1000 MPa or greater.