Which instrument's range is from Bb3 to A6?

The oboe's range extends from B-flat in the third octave (Bb3) to A in the sixth octave (A6), making it a unique instrument in the woodwind family. This range allows the oboe to produce a wide variety of pitches suitable for both melodic lines and harmonic support in ensemble settings. Its distinct timbre and expressiveness are well-suited to both orchestral and solo repertoire, typically sitting above the strings and woodwinds due to its higher register.

In contrast, while the flute and saxophone also possess considerable ranges, their specific ranges differ from that of the oboe. The clarinet, specifically the B-flat clarinet, has a different range and can play lower pitches than the oboe, thus making it distinct in character. Therefore, the oboe is specifically recognized for its ability to cover the range from Bb3 to A6 effectively, aligning perfectly with the requirements stated in the question.