The process whose specific outcome is the progression of a metanephric ascending thin limb over time, from its formation to the mature structure. The metanephric ascending thin limb is a segment of a nephron tubule in the metanephros lying in the inner medulla that is permeable to ions but not to water and has a simple epithelium; active transepithelial solute transport is absent. [ GOC:mtg_kidney_jan10 ]