STROBE-X is a probe-class mission concept designed for X-ray timing and spectroscopy across the 0.2–30 keV band, with enormous collecting area, high throughput, and excellent spectral and temporal resolution. It was proposed in response to the 2023 NASA Astrophysics Probe Explorer call, following the recommendation of the Astro2020 Decadal Survey for an X-ray probe mission.

The observatory comprises three instruments—the Low Energy Modular Array (LEMA), the High Energy Modular Array (HEMA), and a Wide Field Monitor (WFM)—providing transformative capabilities for studying black holes, neutron stars, accretion physics, galaxy clusters, and time-domain and multi-messenger astrophysics.

Selections were announced in October 2024. Although STROBE-X received a Category 1 ranking and a low technical and cost risk rating, it was not selected for a Phase A study.