Phillip Anthony Keys appeals the sentence the district court imposed following Keys’s guilty plea to a drug-conspiracy charge. Counsel has moved to withdraw and filed a brief under Anders v. California, 386 U.S. 738, 87 S.Ct. 1396, 18 L.Ed.2d 493 (1967). In his brief, counsel notes Keys received a reduction in his sentence for substantially assisting the government, but argues the government should have allowed Keys more time to cooperate so Keys could receive an even greater reduction in his sentence. As far as Keys’s reduced sentence is concerned, the extent of the reduction is unreviewable. See United States v. Coppedge, 135 F.3d 598, 599 (8th Cir. 1998) (per curiam). Nevertheless, the plea agreement appears to permit Keys to continue to assist the government and to permit the government to file additional Rule 35(b) motions on his behalf. Finally, having reviewed the record independently in accordance with Penson v. Ohio, 488 U.S. 75, 109 S.Ct. 346,102 L.Ed.2d 300 (1988), and finding no other nonfrivolous issues, we affirm the district court and grant counsel’s motion to withdraw.