  We describe a method to extract an effective Lagrangian description for open
bosonic strings, at zero transcendentality. The method relies on a particular
formulation of its scattering amplitudes derived from color-kinematics duality.
More precisely, starting from a $(DF)^2 + \text{YM}$ quantum field theory, we
integrate out all the massive degrees of freedom to generate an expansion in
the inverse string tension $\alpha^\prime$. We explicitly compute the
Lagrangian terms through $\mathcal{O}(\alpha^{\prime 4})$, and target the
sector of operators proportional to $F^4$ to all orders in $\alpha^\prime$.
