Is a plaintiff's dismissal under Rule 12(b)(6) a dismissal based on sovereign immunity?

^2. Although the district court characterized its dismissal as falling under Rule 12(b)(6), it is more appropriately characterized as a dismissal under Rule 12(b)(1), as it was based on sovereign immunity. See Dube v. State Univ. of N.Y., 900 F.2d 587, 594 (2d Cir. 1990) (explaining the federal courts "lack jurisdiction" over 1983 claims that are barred by Eleventh Amendment immunity (internal quotation marks omitted)).