\[ a \left (-\sqrt {y(x)^2+1}\right )-b+y'(x)=0 \] ✓ Mathematica : cpu = 0.326393 (sec), leaf count = 96
\[\left \{\left \{y(x)\to \text {InverseFunction}\left [\frac {\frac {b \tan ^{-1}\left (\frac {\text {$\#$1} b}{\sqrt {\text {$\#$1}^2+1} \sqrt {a^2-b^2}}\right )}{\sqrt {a^2-b^2}}-\frac {b \tan ^{-1}\left (\frac {\text {$\#$1} a}{\sqrt {a^2-b^2}}\right )}{\sqrt {a^2-b^2}}+\sinh ^{-1}(\text {$\#$1})}{a}\& \right ][x+c_1]\right \}\right \}\] ✓ Maple : cpu = 0.058 (sec), leaf count = 26
\[\left \{c_{1}+x -\left (\int _{}^{y \left (x \right )}\frac {1}{\sqrt {\textit {\_a}^{2}+1}\, a +b}d \textit {\_a} \right ) = 0\right \}\]