The X-ray Integral Field Unit architecture following the Athena mission rescope

The Athena mission underwent a redefinition phase since July 2022, driven by the imperative to reduce the mission cost for the European Space Agency while maintaining its flagship character. This most notably lead to a modification of the X-ray Integral Field Unit (X-IFU) cryogenic architecture. Passive cooling via radiative panels at spacecraft level (V-grooves) now provides a 50K thermal environment to the X-IFU cryostat. 4K cooling is achieved through a remote active cooler, with a multi-stage Adiabatic Demagnetization Refrigerator delivering the final 50 mK temperature required by the detectors. Amidst these changes, the core concept of the readout chain remains robust, utilizing Transition Edge Sensor microcalorimeters and Time-Division Multiplexing. Noteworthy is the introduction of a slower pixel, enabling an increase in the multiplexing factor (from 34 to 48) without compromising the energy resolution. This mitigates the reduction of the field of view (from 5’ to 4’) while reducing the number of channels and thus the resource demands on the system. In this contribution, we will give an overview of this new instrument architecture, addressing its main functional chains.