Structure of $XeO _{3}$ has $3 p \pi- d \pi$ bonds.
Here, $p$-orbital is from $O$ and $d$-orbital is from $Xe$ atom respectively.
Structure of $XeO _{4}$ has $4 p \pi- d \pi$ bonds.
Here, $p$-orbital is from $O$ and $d$-orbital is from $Xe$ atom respectively.