Stress corrosion crack (SCC) initiation testing has been performed on a 15% cold-worked UNS N06600 (Alloy 600) heat in mill-annealed (MA), solution annealed (SA), and thermally treated (TT) conditions to assess the role of grain boundary (GB) carbides on stress-assisted intergranular attack (IGA) and short crack nucleation and growth. The SCC initiation tests were conducted at a constant load equivalent to the materials’ yield stress in 360oC simulated pressurized water reactor primary water. Results revealed the highest SCC initiation susceptibility occurred in the Alloy 600 MA material, followed by the TT and SA materials, suggesting that GB carbide distribution did not have a controlling effect on SCC initiation resistance. Quantitative assessments of IGA and short cracks were conducted to help understand this phenomenon, and the role of GB carbides in precursor damage development that leads to differences in macroscopic SCC initiation behavior are discussed.