Calix (ASX:CXL) reached its first milestone under the Australian Renewable Energy Agency (Arena) grant for the Zesty Green Iron Demonstration Project, according to a Monday Australian bourse filing.

The milestone triggers an initial AU$2 million grant payment, with a further AU$42.9 million contingent on matched funding and subsequent project milestones, per the filing.

The payment comes after a AU$3 million contribution from Rio Tinto Group (ASX:RIO) in December 2025, with more than AU$32 million in additional cash and in-kind support contingent on achieving specific milestones, the filing added.

Calix's shares fell past 5% in recent Monday trade, while Rio Tinto's shares were down almost 2%.