Complex sentence: In 1998, in response to developer comments about the new operating system, the "big announcement" at WWDC'98 was the introduction of "Carbon", effectively a version of the "classic" Mac OS API implemented on OpenStep.
Split into simpler sentences: In 1998, In response to developer comments about the new operating system, the "big announcement" at WWDC'98 was the introduction of "Carbon". Carbon was effectively a version of the "classic" Mac OS API implemented on OpenStep.