\[ a \left (-\sqrt {y(x)^2+1}\right )-b+y'(x)=0 \] ✓ Mathematica : cpu = 0.240022 (sec), leaf count = 96
DSolve[-b - a*Sqrt[1 + y[x]^2] + Derivative[1][y][x] == 0,y[x],x]
\[\left \{\left \{y(x)\to \text {InverseFunction}\left [\frac {\frac {b \tan ^{-1}\left (\frac {\text {$\#$1} b}{\sqrt {\text {$\#$1}^2+1} \sqrt {a^2-b^2}}\right )}{\sqrt {a^2-b^2}}-\frac {b \tan ^{-1}\left (\frac {\text {$\#$1} a}{\sqrt {a^2-b^2}}\right )}{\sqrt {a^2-b^2}}+\sinh ^{-1}(\text {$\#$1})}{a}\& \right ][x+c_1]\right \}\right \}\] ✓ Maple : cpu = 0.057 (sec), leaf count = 26
dsolve(diff(y(x),x)-a*(y(x)^2+1)^(1/2)-b = 0,y(x))
\[x -\left (\int _{}^{y \left (x \right )}\frac {1}{a \sqrt {\textit {\_a}^{2}+1}+b}d \textit {\_a} \right )+c_{1} = 0\]