The stable hull of an exact $\infty$-category

Abstract: We construct a left adjoint $\mathcal{H}^\text{st}\colon \mathbf{Ex}{\infty} \rightarrow \mathbf{St}{\infty}$ to the inclusion $\mathbf{St}{\infty} \hookrightarrow \mathbf{Ex}{\infty}$ of the $\infty$-category of stable $\infty$-categories into the $\infty$-category of exact $\infty$-categories, which we call the stable hull. For every exact $\infty$-category $\mathcal{E}$, the unit functor $\mathcal{E} \rightarrow \mathcal{H}^\text{st}(\mathcal{E})$ is fully faithful and preserves and reflects exact sequences. This provides an $\infty$-categorical variant of the Gabriel-Quillen embedding for ordinary exact categories. If $\mathcal{E}$ is an ordinary exact category, the stable hull $\mathcal{H}^\text{st}(\mathcal{E})$ is equivalent to the bounded derived $\infty$-category of $\mathcal{E}$.