Are the RLS filter and Kalman filter gradient methods?
Recursive least squares (RLS) filters don't use gradient descent. As their name suggests, they use a least-squares fit to determine the optimum coefficients at each time step. Via clever formulation of the filter structure, one can use the calculations done from time step $n$ to recursively calculate the updated coefficients for time step $n+1$ without having to do the full least-squares fit again.