Focused Multitasker

Prerequisite: 8 levels of spellcaster

Your extensive experience as a spellcaster has honed your ability to focus.

Increase your either your Constitution score or your spellcasting ability score by 1, to a maximum of 20.

You have the ability to concentrate on up to two spells simultaneously; casting a second concentration spell doesn't automatically end one concentration spell already active. The sum of the levels of the spells cast must be no greater than the level of your highest-level spell slot, and you are unable to concentrate on two iterations of the same spell (e.g., Bless on a set of allies and also Bless on a different set of allies). This feat can apply to concentrating on a readied spell but does not apply to non-spell abilities or non-spell effects that happen to require concentration (e.g., Invoke Duplicity).

When you cast a spell that requires concentration while already attempting to maintain concentration on an active spell, you must make a concentration check with a DC of 5 plus the level of the already active spell. On a successful check, both spells become active and require concentration. On an unsuccessful check, that spell slot is consumed, and you maintain concentration on your choice of only one of the two spells.
If, while you are concentrating on two spells, you cast a third spell that requires concentration, you must choose which of the first two spells to end before performing this check.

If, while you are concentrating on two spells, you are required to pass a concentration check in order to maintain concentration, you perform only one check as if concentrating on only one spell. On an unsuccessful check, both spells end.