Redshift evolution of the size–mass relation slope α (top panel) and intrinsic scatter σ (log R_e) (bottom panel) for BGGs classified using color (solid lines), sSFR (dashed lines), and consensus (dotted lines) methods. Star-forming and quiescent BGGs are shown in blue and red, respectively. Quiescent BGGs display consistently steeper slopes, especially at z ∼ 1–3, while star-forming BGGs maintain nearly flat relations across redshift. The scatter increases toward higher redshift for both types, indicating greater structural diversity and formation variability in the early universe.