A preprint posted to arXiv in May 2026 details the first multi-mission campaign on the Galactic black-hole transient GS 1354-64 during its 2025-26 outburst. MAXI provided daily all-sky monitoring, while NuSTAR and Insight-HXMT delivered pointed broadband spectra that captured two flares peaking at 1.4 and 0.8 Crab. The source traversed canonical hard-to-soft states on the hardness-intensity diagram, yet the return path deviated sharply—an asymmetry the authors attribute to changes in the inner accretion flow rather than simple hysteresis. Quasi-periodic oscillations swept from 0.07 to 4 Hz during the hard and intermediate states, modeled via the propagating oscillatory shock framework; the shock radius appears to contract then expand on timescales of days, offering a direct probe of disk-corona coupling. Spectral fits with diskbb plus relxill components yield a spin parameter a_k approximately 0.998 and inclination 63-70 degrees, consistent with earlier 2010s reports but now derived from higher-signal-to-noise data. This work remains a preprint and has not undergone peer review; the analysis rests on a single outburst of one source, with model-dependent assumptions about disk truncation and reflection geometry. Related studies of GX 339-4 (e.g., Motta et al. 2015, MNRAS) show similar rapid QPO drifts, while NuSTAR campaigns on MAXI J1820+070 (Fabian et al. 2020, MNRAS) demonstrate how reflection features can constrain spin even when the soft-state decay is truncated. The present observations therefore strengthen the case that near-maximal spins are common among transients yet leave open whether the anomalous HID path signals a temporary change in magnetic field topology or an undetected jet-launching episode.