Einstein Telescope (ET) will be sensitive to detect hundreds of thousands of individual astrophysical sources out to cosmological distances, as well as the stochastic gravitational-wave background (SGWB) of astrophysical or cosmological origin. Two baseline designs are under consideration: a single triangular interferometer and a pair of L-shaped detectors. Each geometry offers distinct advantages and challenges for different science goals.

In this talk, I will first review the ET’s potential to probe key questions in both early- and late-time cosmology. I will then present a recent study of how correlated seismic noise impacts the ability to detect a low-frequency SGWB. Using simulated SGWB data, I will present results from a Bayesian analysis to quantify biases that arise when noise correlations are neglected. Finally, I will discuss the SGWB-search performance of the triangular design against the 2-L configuration, highlighting differences in parameter estimation in the presence of correlated noise.