KSeF Updates in Poland: Attachment Notifications and Production Environment Shutdown

As the transition to the mandatory National e-Invoicing System (KSeF) accelerates, Polish authorities have introduced a new notification requirement for invoices containing attachments, effective January 14, 2026. Concurrently, the Ministry of Finance has confirmed a critical maintenance schedule that effectively ends the operational life of the KSeF 1.0 production environment on January 26, 2026.

New Protocol for Invoice Attachments

Starting January 14, 2026, taxpayers intending totaxpayers intending to utilize technical attachment nodes within the FA(3) XML structure must first submit a formal notification to the tax authority. This requirement specifically addresses industries such as utilities and telecommunications, where complex billing data often accompanies the primary tax document.

The Notification Process

Businesses cannot simply begin attaching files. The new protocol requires:

• Prior Declaration: Taxpayers must register their intent to issue invoices with attachments via the e-Tax Office before utilizing the feature.
• Scope Limitation: Attachments are strictly limited to tax-related data (e.g., consumption logs, unit price breakdowns). Non-tax content, such as marketing materials or general contracts, is explicitly prohibited.
• Approval Time: The tax authority reserves up to three business days to process and confirm these notifications.

KSeF 1.0 Sunset and Maintenance Break

To prepare for the full launch of KSeF 2.0, the Ministry has scheduled a definitive maintenance window that will shut down the current KSeF 1.0 system.

Critical Dates for Taxpayers

• January 26, 2026 (Deadline): This is the final day taxpayers can utilize the current KSeF 1.0 production environment. All necessary actions in the current system, including generating legacy tokens or finalizing 1.0 transactions, should be completed by the end of the day on January 25.
• January 26 – 31, 2026 (Blackout Period): A scheduled technical maintenance break will render the KSeF 1.0 environment, including the Certificate and Authorizations Module (MCU), completely unavailable.
• February 1, 2026 (Go-Live): The KSeF 2.0 production environment will officially go live, becoming the sole mandatory system for large taxpayers.

Businesses currently using KSeF 1.0 must ensure their systems are ready to switch over to the 2.0 API immediately following the blackout period to maintain compliance.

There’s more you should know about e-invoicing in Poland – learn more about the new and upcoming regulations.