Initiallty, 50 – 60 million of the new notes will be put into circulation, with the old notes gradually being taken out of circulation.
The old notes will still be legal tender.
The new note will also be red in colour and 72 x 150mm in size will feature a portrait of King Rama IX in the Royal House of Chakri gown on the front, whilst the back will show an image of King Taksin the Great
https://www.bot.or.th/Thai/PressandSpeeches/Press/News2558/n1058e.pdf