Koolen–Gebremichel conjecture on primitive strongly regular graphs with smallest eigenvalue −3

Let $G$ be a primitive strongly regular graph with parameters $(n,k,\lambda,\mu)$ and smallest eigenvalue $-3$.

Koolen–Gebremichel conjecture. Either $\mu\in\{6,9\}$ or $n\leqslant 276$.

The conjecture concerns the remaining feasible parameter sets for primitive strongly regular graphs with smallest eigenvalue $-3$. The paper establishes nonexistence for the parameters $(1911,270,105,27)$, but the broader conjecture remains open.