\[ y'(x)=\frac {e^{-2 x} y(x)^3}{e^{-x} y(x)+1} \] ✓ Mathematica : cpu = 0.664958 (sec), leaf count = 78
DSolve[Derivative[1][y][x] == y[x]^3/(E^(2*x)*(1 + y[x]/E^x)),y[x],x]
\[\text {Solve}\left [\log (y(x))+y(x)^2 \left (\frac {x}{y(x)^2}-\frac {\log \left (-y(x)^2+e^x y(x)+e^{2 x}\right )}{2 y(x)^2}+\frac {\tanh ^{-1}\left (\frac {y(x)+2 e^x}{\sqrt {5} y(x)}\right )}{\sqrt {5} y(x)^2}\right )=c_1,y(x)\right ]\] ✓ Maple : cpu = 0.866 (sec), leaf count = 58
dsolve(diff(y(x),x) = 1/(y(x)*exp(-x)+1)*y(x)^3*exp(-2*x),y(x))
\[y \left (x \right ) = {\mathrm e}^{\RootOf \left (2 \sqrt {5}\, \arctanh \left (\frac {\left (-2 \,{\mathrm e}^{\textit {\_Z}}+{\mathrm e}^{x}\right ) \sqrt {5}\, {\mathrm e}^{-x}}{5}\right )+5 \ln \left (-{\mathrm e}^{2 x}-{\mathrm e}^{\textit {\_Z} +x}+{\mathrm e}^{2 \textit {\_Z}}\right )+10 c_{1}-10 \textit {\_Z} -10 x \right )}\]