Does a defendant's failure to request an instruction on theft constitute forfeiture?

We reject the People's forfeiture argument. Appellant's only claim here is that the trial court had a sua sponte duty to instruct on theft as a lesser included offense of robbery. The trial court is obligated to instruct on lesser included offenses sua sponte, even if as a matter of trial tactics a defendant not only fails to request the instruction but expressly objects to its being given. (People v. Breverman (1998) 19 Cal.4th 142, 154 (Breverman).) The failure to request an instruction on a lesser included offense cannot therefore forfeit the claim that the trial court was required to give the instruction sua sponte.