We present the globally available dataset of Line-of-sight Gravity Differences (LGD) as a new data product to fill the long-standing gap of investigating sub-monthly surface mass change from the satellite gravimetry along-track perspective. The dataset is generated directly from Gravity Recovery and Climate Experiment Follow-on (GRACE-FO) Level-1B intersatellite ranging observations, positioned conceptually between Level-1B measurements and Level-2 monthly gravity field solutions. Provided as along-track time series, LGD delivers instantaneous, in situ gravity change at satellite altitude, thus ensuring the fidelity of measurements by avoiding the complex preprocessing, regularization, and filtering applied to monthly products. The LGD dataset enables monitoring of sub-monthly terrestrial water storage variability and provides accurate information on timing and magnitude of water mass changes. GRACE-FO’s ground track allows LGD retrievals every 5–6 days in most low and mid latitude regions, while the revisit interval becomes shorter toward higher latitudes. Our LGD data products also contain climatology in the form of along-track gravity variations. We demonstrate its potential through case studies, including along-track diagnosis of flash drought evolution in the southeastern United States and the characterization of sub-monthly hydrological extremes in global hotspots. Results show that the LGD dataset resolves the critical timing (onset, peak, and termination) of hydrological extremes, which is unattainable from monthly products. The LGD dataset is available at <a href="https://doi.org/10.5281/zenodo.17766177" target="_blank" rel="noopener">https://doi.org/10.5281/zenodo.17766177</a> (Tang et al., 2025), which is expected to pave the way for advances in sub-monthly hydrological monitoring and can serve as a unique constraint for hydrological and geophysical models, opening new opportunities for Earth system sciences.