We consider the Gerdjikov‐Ivanov–type derivative nonlinear Schrödinger equation
iqt+qxx−iq2q¯x+12|qfalse|4−q04q=0
on the line. The initial value q(x,0) is given and satisfies the symmetric, nonzero boundary conditions at infinity, that is, q(x,0)→q± as x→±∞, and |q±|=q0>0. The goal of this paper is to study the asymptotic behavior of the solution of this initial value problem as t→∞. The main tool is the asymptotic analysis of an associated matrix Riemann‐Hilbert problem by using the steepest descent method and the so‐called g‐function mechanism. We show that the solution q(x,t) of this initial value problem has a different asymptotic behavior in different regions of the xt‐plane. In the regions
x<−22q02t and
x>22q02t, the solution takes the form of a plane wave. In the region
−22q02t