Here is today’s opinion in Vann v. Dept. of Interior: CADC Opinion

An excerpt:

Applying the precedents that permit suits against government officials in their official capacities, we conclude that this suit may proceed against the Principal Chief in his official capacity, without the Cherokee Nation itself as a party.
The Freedmen have sued the Principal Chief in his official capacity under the doctrine of Ex parte Young, 209 U.S. 123. The Ex parte Young doctrine allows suits for declaratory and injunctive relief against government officials in their official capacities – notwithstanding the sovereign immunity possessed by the government itself. The Ex parte Young doctrine applies to Indian tribes as well. Cf. Oklahoma Tax Commission, 498 U.S. at 514; see generally Larson, 337 U.S. at 689-92; RICHARD H. FALLON, JR., DANIEL J. MELTZER & DAVID L. SHAPIRO, HART AND WECHSLER’S THE FEDERAL COURTS AND THE FEDERAL SYSTEM 958-60 (5th ed. 2003).

Briefs are here.