\[ y'(x)-f(a x+b y(x))=0 \] ✓ Mathematica : cpu = 0.184785 (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 = 0.032 (sec), leaf count = 37
\[ \left \{ y \left ( x \right ) ={\frac {{\it RootOf} \left ( \int ^{{\it \_Z}}\! \left ( f \left ( {\it \_a}\,b \right ) b+a \right ) ^{-1}{d{\it \_a}}b-x+{\it \_C1} \right ) b-ax}{b}} \right \} \]