From the documentation:
The
@(at) operator is intended to be used for matrix multiplication. No builtin Python types implement this operator.
The @ operator was introduced in Python 3.5. @= is matrix multiplication followed by assignment, as you would expect. They map to __matmul__, __rmatmul__ or __imatmul__ similar to how + and += map to __add__, __radd__ or __iadd__.
The operator and the rationale behind it are discussed in detail in PEP 465.