Brussels: The CBAM definitive period began on 1 January 2026, and it turned the EU’s carbon border mechanism from a reporting exercise into a payment obligation for importers. Under Regulation (EU) 2023/956, companies that bring steel, cement, fertilisers and similar goods into the Union now carry a financial cost for the emissions embedded in them.

This analysis explains who must act, how the small-importer exemption works, and what the customs declaration now requires, based on the Commission’s Access2Markets guidance published on 28 January 2026.

What the CBAM definitive period changed

During the transitional phase, importers only reported emissions. The CBAM definitive period replaces that with three duties. Importers must register in advance as authorised declarants with their national authority. They must buy CBAM certificates to cover embedded emissions. And an accredited verifier must check the emissions data.

The Commission describes full implementation by 2034. The guidance page reviewed does not state when certificate sales begin or how certificates are priced, so those details need a separate source.

The 50-tonne threshold

A de minimis rule shields occasional small importers. It applies to the total net mass of goods across all tariff codes, aggregated per importer and per calendar year, and the limit is 50 tonnes. A dedicated customs code, 137, marks these imports. The rule does not cover hydrogen and electricity.

For many small firms, the CBAM definitive period will therefore hinge on a simple tonnage count. An importer that crosses the line mid-year loses the exemption and must register as an authorised declarant.

New customs declaration codes

Since the start of the year, every import declaration must carry one CBAM-related code in the additional reference field of the new EU import system. Codes include Y128 for the CBAM account number, Y238 for an application reference, 137 for the de minimis case, and Y237 for goods of EU origin. Further codes cover inward processing and specific territories such as Büsingen, Heligoland and Livigno.

The customs declaration is where the CBAM definitive period meets daily trade. These codes look technical, but they decide whether a consignment clears smoothly. A wrong or missing code can delay goods at the border, so customs brokers need updated systems.

What importers should do now

Companies should confirm whether they pass the 50-tonne threshold, register if they do, and secure verified emissions data from suppliers outside the Union. Suppliers in third countries face pressure as well, because buyers will ask them for reliable data.

Finance teams should also budget for certificate costs, since the payment duty is the real shift of the CBAM definitive period. The guidance reviewed does not give a price, so any forecast of the bill would be speculation. Procurement teams, in turn, can compare suppliers on verified emissions data, which turns carbon intensity into a purchasing criterion.

The sources reviewed give no information on how far the CBAM definitive period will extend to downstream products, and that question remains open. For now, importers should treat the CBAM definitive period as a standing compliance duty that rewards early preparation.