We present new stellar mass functions at $zsim6$, $zsim7$, $zsim8$, $zsim9$ and, for the first time, $zsim10$, constructed from $sim800$ Lyman-Break galaxies previously identified over the XDF/UDF, parallels and the five CANDELS fields. Our study is distinctive due to (1) the much deeper ($sim200$ hour) wide-area Spitzer/IRAC imaging at $3.6mu$m and $4.5mu$m from the GOODS Re-ionization Era wide Area Treasury from Spitzer (GREATS) program and (2) consideration of $zsim6-10$ sources over a $3times$ larger area than previous HST+Spitzer studies. The Spitzer/IRAC data enable $ge2sigma$ rest-frame optical detections for an unprecedented $50%$ of galaxies down to a stellar mass limit of $sim10^{8}mathcal{M}_odot$ across all redshifts. Schechter fits to our volume densities suggest a combined evolution in characteristic mass $mathcal{M}^*$ and normalization factor $phi^*$ between $zsim6$ and $zsim8$. The stellar mass density (SMD) increases by $sim1000times$ in the $sim500$ Myr between $zsim10$ and $zsim6$, with indications of a steeper evolution between $zsim10$ and $zsim8$, similar to the previously-reported trend of the star-formation rate density. Strikingly, abundance matching to the Bolshoi-Planck simulation indicates halo mass densities evolving at approximately the same rate as the SMD between $zsim10$ and $zsim4$. Our results show that the stellar-to-halo mass ratios, a proxy for the star-formation efficiency, do not change significantly over the huge stellar mass build-up occurred from $zsim10$ to $zsim6$, indicating that the assembly of stellar mass closely mirrors the build-up in halo mass in the first $sim1$ Gyr of cosmic history. JWST is poised to extend these results into the first galaxy epoch at $zgtrsim10$.
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