We study whether an open FLRW universe with a negative cosmological constant can evade the eventual recollapse characteristic of an anti–de Sitter (AdS)-type universe. Within a power-law realization of fab-four theory, we solve the background equations numerically and analyze the asymptotic dynamics. For the representative branch and parameter choice studied here, we find that the scalar sector provides a self-tuninglike compensation for the negative $\mathrm{\Lambda }$, while the curvature term remains unscreened. As a result, the universe can continue expanding instead of recollapsing. Instead, the universe evolves toward a curvature-dominated linear-expansion regime, $a\propto t$. To probe the underlying compensation mechanism, we further analyze an auxiliary zero-curvature subsystem using Poincaré compactification. In the $\mathrm{\Lambda }<0$ domain, there exist background trajectories that approach a critical point at infinity. Near this point, the compensating scalar-$\mathrm{\Lambda }$ sector becomes stifflike, $w_{\varphi +\mathrm{\Lambda }}\to 1$, so that the system effective energy density redshifts faster than curvature ($w_k=-1/3$). Although this auxiliary analysis does not cover the full curved cosmology, it is consistent with and qualitatively supports the numerical finding that the net $\varphi +\mathrm{\Lambda }$ contribution becomes subdominant to curvature, thereby preventing recollapse despite $\mathrm{\Lambda }<0$. This extends the application of the self-tuning mechanism to the AdS region and offers a possibility for the AdS Universe predicted by string theory to become a reality.

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• Alternative gravity theories
• Cosmology