SEDs for four gamma-ray blazars: 3C 279 (a typical FSRQ, top); W Com (a low energy peaked BL Lac object, LBL) and PKS 2155-304 (an high energy peaked BL Lac object, HBL) middle; M 87 (a FR-I radio galaxy, bottom). Included in the SEDs are multiwavelentgh data points collected in different epochs (different brightness states) for each sources (errors bars not represented for clarity). A qualitative representation of the average expected LAT passband and sensitivity for 1 year of observations is shown.