iOS 9.3 is coming in the Spring and will introduce Night Shift as well as a number of other new features.
Tim Cook Live on Stage at D11: All Things Digital Tonight
Cook participated in the event for the first time last year with a 100-minute interview with Walt Mossberg and Kara Swisher. Cook's predecessor, Steve Jobs, also participated in the D conferences on a number of occasions.
Cook is not expected to make any major announcements during his interview, but he is likely to provide some insight into Apple's business and the markets in which the company participates. Tidbits from his appearance last year included discussion of how Apple was going to "double down" on product secrecy in order to fight leaks, a brief mention of Apple's interest in TV, and hints at the Facebook integration that arrived in iOS 6 and improvements to Siri.