\[ a \left (-\sqrt {y(x)^2+1}\right )-b+y'(x)=0 \] ✓ Mathematica : cpu = 0.188531 (sec), leaf count = 96
\[\left \{\left \{y(x)\to \text {InverseFunction}\left [\frac {\frac {b \tan ^{-1}\left (\frac {\text {$\#$1} b}{\sqrt {\text {$\#$1}^2+1} \sqrt {a^2-b^2}}\right )}{\sqrt {a^2-b^2}}-\frac {b \tan ^{-1}\left (\frac {\text {$\#$1} a}{\sqrt {a^2-b^2}}\right )}{\sqrt {a^2-b^2}}+\sinh ^{-1}(\text {$\#$1})}{a}\& \right ]\left [c_1+x\right ]\right \}\right \}\]
✓ Maple : cpu = 0.09 (sec), leaf count = 26
\[ \left \{ x-\int ^{y \left ( x \right ) }\! \left ( a\sqrt {{{\it \_a}}^{2}+1}+b \right ) ^{-1}{d{\it \_a}}+{\it \_C1}=0 \right \} \]