\[ y'(x)-f(a x+b y(x))=0 \] ✓ Mathematica : cpu = 0.236357 (sec), leaf count = 248
\[\text {Solve}\left [\int _1^{y(x)}-\frac {f(a x+b K[2]) \int _1^x\left (\frac {b^2 f'(a K[1]+b K[2])}{a+b f(a K[1]+b K[2])}-\frac {b^3 f(a K[1]+b K[2]) f'(a K[1]+b K[2])}{(a+b f(a K[1]+b K[2]))^2}\right )dK[1] b+b+a \int _1^x\left (\frac {b^2 f'(a K[1]+b K[2])}{a+b f(a K[1]+b K[2])}-\frac {b^3 f(a K[1]+b K[2]) f'(a K[1]+b K[2])}{(a+b f(a K[1]+b K[2]))^2}\right )dK[1]}{a+b f(a x+b K[2])}dK[2]+\int _1^x\frac {b f(a K[1]+b y(x))}{a+b f(a K[1]+b y(x))}dK[1]=c_1,y(x)\right ]\] ✓ Maple : cpu = 0.046 (sec), leaf count = 37
\[\left \{y \left (x \right ) = \frac {-a x +b \RootOf \left (b \left (\int _{}^{\textit {\_Z}}\frac {1}{b f \left (\textit {\_a} b \right )+a}d \textit {\_a} \right )+c_{1}-x \right )}{b}\right \}\]