Posterior distribution in the S₈-Ω_m plane for the combination of KiDS-Legacy, DESI DR2 BAO, eBOSS DR16 RSD, and Planck 2018 TTTEEE, low-ℓ TT, and low-ℓ EE datasets. The blue contours illustrate the posterior inferred in a Horndeski model parametrised by the stable basis parameters ${\widehat{D}}_{\mathrm{kin}}$ and $\mathrm{\Delta }{\widehat{M}}_{\ast }^2$, and the green contour shows constraints from sampling ${\widehat{D}}_{\mathrm{kin}}$ and ${\widehat{c}}_{\mathrm{s}}^2$. The orange contour shows the posterior in a Horndeski model using the ${\widehat{\alpha }}_{\mathrm{B}}$-${\widehat{\alpha }}_{\mathrm{M}}$ parametrisation. The black contour corresponds to the fiducial ΛCDM analysis. The inner and outer contours of the marginalised posteriors correspond to the 68% and 95% credible intervals, respectively.