From Ydun's Medium Wave Info.

"Closure date for BBC Radio 4 longwave on 198 kHz will be 26 September 2026 Arqiva staff have been informed.
It’s not yet known if the transmitters will remain on air for the Radio Teleswitch Service after this date, or if that will end at the same time. (ref: British DX Club “Communication” magazine August 2025).
So in 13 months time. But could stay on air without R4 programming after this (as Allouis 162 kHz has)?"