This issue is a variant of X-Men Annual (Marvel, 1970 series) #4 [Direct].
Features a page of letters devoted to the Dark Phoenix saga.; indicia title: X-Men™ Annual Vol. 1 No. 4; cover title: King-Size Annual! X-Men™
References to Dante's Inferno. Story depicts events leading directly to Nightcrawler's first appearance in Giant-Size X-Men #1. Published between X-Men #138 and 139.