FLASH, the free-electron laser user facility at DESY, delivers XUV and soft X-ray radiation for photon experiments since 2005. It is driven by a superconducting linear accelerator, and has two undulator lines (FLASH1 and FLASH2). A third electron beam line hosts the plasma wakefield experiment FLASHForward. Presently, the FLASH facility is undergoing an extensive refurbishment and a substantial upgrade (FLASH2020+). In this paper we summarize the FLASH operation in 2019 - 2021, and report on the main upgrades realized in a long installation shutdown from November 2021 to summer 2022.

The FLASH2020+ project has started to transform the FLASH facility to broaden the facility profile and meet demands of future user experiments. In a nine-month lasting shutdown until August 2022 the linear accelerator of the FLASH facility has, among others, been upgraded with a laser heater, new bunch compressors and new modules. The latter results in an energy upgrade to 1.35 GeV allowing to reach sub 4 nm wavelength. In the following 14-month lasting shutdown starting mid 2024 the FLASH1 FEL beamline will be completely rebuild. The design is based on external seeding at MHz repetition rate in burst mode allowing for coherent tuneable FEL radiation in wavelength and polarization by installation new APPLE-III undulators. Post compression of the beam downstream of the radiators will allow for high quality THz generation and together with the new experimental endstations and pump probe lasers provide a unique portfolio for next generation user experiments.