Can a commander with partner have a different partner commander in the command zone at the same time?

The Partner ability (CR 702.124) is a keyword that explicitly allows you to have two commanders in the command zone at the start of the game, provided both commanders have the Partner keyword. Normally, the Commander format rule (CR 903.3) permits exactly one commander, but Partner creates a specific exception to this rule.

Both commanders must individually have the Partner keyword (or a compatible variant such as "Partner with [specific name]"). If only one of the two commanders has Partner and the other does not, the pair is not legal — both must have the ability (CR 702.124a).

During the game, each partner commander follows all the usual commander rules independently: each has its own commander damage tracking (21 damage from a single commander is lethal), each can be cast from the command zone for its own commander tax, and each contributes to defining your deck's color identity (CR 903.4).

Example: You start the game with both Tymna the Weaver and Thrasios, Triton Hero in your command zone. Both have Partner, so this is legal. Your color identity is White, Black, Green, and Blue. If Tymna is destroyed, you may recast her from the command zone for {2} extra (her commander tax), while Thrasios remains on the battlefield unaffected.

Note that "Partner with [Name]" (a variant from Battlebond) only pairs with its specific named partner, not any other partner commander — so a "Partner with" card cannot pair with a generic Partner card (CR 702.124f).