The EU Carbon Border Adjustment Mechanism entered its definitive financial phase on January 1, 2026, making carbon costs real and immediate for steel importers. Default emission values can cost two to four times more than verified actual data, translating into millions of euros in avoidable expense. Key compliance deadlines fall in 2027, including certificate purchases from February and final declarations by September. The UK launches its own parallel mechanism in January 2027, creating a dual compliance burden for exporters serving both markets.