The double Olympic champion replaces Katie Ledecky from the USA.
Titmus improved the world record over 400 m freestyle at the Australian swimming championships in Adelaide on Sunday.
The 21-year-old struck in 3: 56.40 minutes and was six hundredths of a second faster than the seven-time Olympic champion Katie Ledecky (USA/3: 56.46) at their gold triumph at the summer games 2016 in Rio de Janeiro.
In 2021, Titmus and Ledecky dominated the Olympic races on the freestyle routes beyond 100 m.
Titmus won over the 200 and 400 m, Ledecky over the 800 and 1500 m.