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We are now in an era of exoplanet characterization. Exoplanets are being intensively studied to measure the abundances of water and other metals in their atmospheres in order to place constraints on the location of their origin within a disk. Inflated sub-Saturn-mass planets bridge the divide between super-Earths and Jupiters comma so constraints on their atmospheric composition and metallicities are particularly important for informing planet formation models. Here comma we propose to perform a detailed investigation of the atmosphere of the hot and extremely inflated sub-Saturn-mass planet KELT-11b. This is one of the best planets to study thanks to its very bright host comma low mass and surface gravity comma and high equilibrium temperature. An HST-WFC3 G141 transmission spectrum indicates that KELT-11b has a clearly sub-solar metallicity atmosphere comma but additional data are needed to determine just how metal-poor the atmosphere is. The proposed observations to measure KELT-11b.s transmission spectrum in the G102 band will not only lead to more precise metallicity constraints but will also reveal whether KELT-11b followed a rare planet formation pathway if the planet.s metallicity is indeed ultra-low. In addition comma with precise atmospheric metallicity constraints for the sub-Saturn-mass KELT-11b comma we will be able to empirically test correlations between planet mass-planet metallicity and between stellar metallicity-planet metallicity. The proposed observations of KELT-11b will ultimately add to a comparative study with the other inflated sub-Saturns discovered to date that can be used to better inform planet formation and evolution models as well as future observations with JWST.