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The cross section for pair-production depends strongly on the total center-of-momentum energy of the reaction. Gamma-rays detected by ground-based telescopes (with energy E >>~ 200 GeV) are subject to strong attenuation by the near- and mid-infrared part of the EBL, limiting O(>100 ~>100 GeV) probes of the EBL to relatively low redshifts (z<~0.5). GLAST, on the other hand, is sensitive to the less drastic attenuation by the UV-optical part of the EBL, with no attenuation expected (at any redshift) for photons with energy below 10 GeV. Thus, EBL attenuation will not limit GLAST's ability to detect distant gamma-ray sources.
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