The favorable energy configurations of nuclei at magic numbers of $N$ neutrons and $Z$ protons are fundamental for understanding the evolution of nuclear structure. The $Z=50$ (tin) isotopic chain is a frontier for such studies, with particular interest at and around the doubly magic ${}^{100}\mathrm{Sn}$ isotope, for which the mass is a topic of debate. Precise mass values for neutron-deficient isotopes provide necessary anchor points for mass models to test extrapolations near the proton drip line, where experimental studies remain out of reach. In this work, we report a Penning trap mass measurement of ${}^{101}\mathrm{Sn}$. The determined mass excess of $-59889.89\left(96\right)$ keV for ${}^{101}\mathrm{Sn}$ represents a factor-of-300 improvement over the current precision and indicates that ${}^{101}\mathrm{Sn}$ is less bound than previously thought. Mass predictions from a recently developed Bayesian model combination framework employing statistical machine learning and nuclear masses computed within seven global models based on nuclear density functional theory agree within $1\sigma$ with experimental masses from the $48\le Z\le 52$ isotopic chains. The framework's resilience to new mass data gave confidence in the extrapolation of tin masses down to $N=46$. Our calculations suggest that ${}^{96}\mathrm{Sn}$ is a two-proton drip line nucleus and predict a mass excess of $-58090\left(800\right)$ keV for ${}^{100}\mathrm{Sn}$, showing a preference within $1\sigma$ for the mass of ${}^{100}\mathrm{Sn}$ derived from the $\beta$-delayed $Q$ value measured at GSI.

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• Binding energy & masses
• Nuclear binding
• Nuclear structure & decays
• 90 ≤ A ≤ 149
• Bayesian methods
• Machine learning categories
• Nuclear density functional theory
• Spectrometers & spectroscopic techniques