The GW2 gene is a growth repressor in cereals. The precise mechanism by which GW2 constrains growth remains unclear in cereals. A set of Near Isogenic Lines (NILs) with a combination of knockout mutations in the three homoeologous copies increase grain size and width with respect to the wildtype control (Paragon WT; Wang et al., 2018). We hypothesize that gibberellins (GA) are involved in the bigger grain size phenotype of gw2 triple mutants. To test this hypothesis, we conducted a glasshouse experiment across two years using Paragon (WT) and Paragon triple gw2 mutant (MT) with contrasting grain sizes phenotypes. Plants were treated with GA, Paclobutrazol (PAC), and a combined treatment PAC+GA. PAC decreased grain weight (-18%), width (-7.5%), and length (-2.9%) only in the MT. However, the large grain size phenotype of the MT could be partially rescued by the addition of GA at flowering (PAC+GA treatment). This result suggests that GAs are required for the Paragon gw2 triple mutant to express its bigger grain size phenotype. Furthermore, the single, double and triple mutants NILs were evaluated across three growing seasons 2019, 2020 and 2021 in UK. Thousand grain weight (TGW) increased consistently in a dosage dependent manner: 2.8% in the single, 9.6% in the double, and 21.4% in the triple mutants. Similarly, grain width increased by 1.7%, 3.7% and 7.6% and length by 1.4%, 3.1% and 7.2%., respectively. Yield, however, did not increase in the single and doubles while in the triple mutants yield decreased significantly by 4.6%. We conclude that the gw2 mutant alleles are beneficial to breed for larger grains. To circumvent the yield losses of the triple mutants under UK conditions, double mutants could be used to strike a balance between increased grain weight and stable yield.