Executive summary

On 8 September 2026, the Luxembourg tax authorities published a new Common Reporting Standard (CRS) User Manual. From 1 January 2027, the User Manual will supplement and replace Circular ECHA No. 4 of 10 August 2020 as the principal practical guidance governing CRS reporting submissions. The User Manual integrates the new AEOI_LUX_V3.0.xsd schema and consolidates and expands the operational guidance applicable to CRS reporting submissions. The migration to AEOI_LUX_V3.0 aligns Luxembourg reporting with Organisation for Economic Co-operation and Development (OECD) CRS XML Schema Version 3.0.

In addition, the tax authorities announced key implementation milestones and updated their CRS Frequently Asked Questions (FAQ). These milestones include the launch of a dedicated pre-validation environment in October 2026. Reporting entities may use the transition period before 1 January 2027 to assess whether updates to their data management frameworks, reporting processes or XML reporting systems are required to accommodate the new schema requirements.

Background

Luxembourg reporting entities are required to electronically submit CRS information to the Luxembourg tax authorities using the prescribed XML reporting format.

Since 2020, Circular ECHA No. 4 has served as the principal source of practical guidance governing submitting, validating and correcting CRS reports. The newly released User Manual replaces that circular and updates the Luxembourg CRS framework by migrating from the previous Luxembourg reporting schema to AEOI_LUX_V3.0, thereby aligning with OECD CRS XML Schema Version 3.0.

New framework

The AEOI_LUX_V3.0 framework combines:

• The OECD CRS reporting data structure
• Luxembourg-specific reporting identifiers and control fields
• Depositor and Reporting Financial Institution (RFI) identification information
• Luxembourg-specific validation and status-message mechanisms

AEOI_LUX_V3.0 is not a standalone Luxembourg reporting framework. It implements the OECD CRS XML Schema Version 3.0 in Luxembourg and supplements it with domestic identification, validation and transmission requirements established by the tax authorities.

Key change: Implementation of new AEOI_LUX_V3.0 schema

Beginning on 1 January 2027, the new AEOI_LUX_V3.0.xsd schema must be used for CRS submissions. The new schema combines the updated OECD CRS XML Schema Version 3.0 with the Luxembourg-specific reporting envelope used by the tax authorities for submission, validation and processing purposes.

Additional developments

Reworked correction mechanism

The User Manual substantially expands, modernizes and clarifies the practical guidance on correcting, canceling and amending previously submitted CRS reports. The revised examples address situations commonly encountered in practice, including changes in tax residence, additions of omitted information and corrections of previously corrected records.

Updated jurisdiction coding and reporting identifiers

The User Manual updates certain jurisdiction codes and provides more detailed guidance on constructing and using reporting identifiers. It also explains the Luxembourg reporting envelope in greater detail, including the structure of AEOI_RefIds, MessageRefIds, DocRefIds and RFI identifiers.

Increased maximum file size

The tax authorities increased the maximum permitted XML file size from 60 MB to 250 MB prior to compression and encryption. According to the User Manual, this change is intended to reduce the need to split large CRS reporting files.

More practical validation guidance

The new User Manual places greater emphasis on the practical operation of the validation process and the interpretation of status messages generated by the tax authorities. In particular, it clarifies the consequences of the different validation outcomes and the information available to identify affected records and data elements. This should help reporting entities diagnose submission errors and warnings more readily and take the appropriate corrective or resubmission action.

Updated FAQ

The revised FAQ amends four existing answers and adds a question on the reporting treatment of undocumented accounts.

The changes focus primarily on reporting and operational aspects of the CRS framework, including:

• Reference material that should be relied on from 2027
• Processing and validation of submitted CRS reports
• Identification requirements for RFIs that do not possess a Luxembourg tax identification number
• Use of substitute taxpayer identification number codes
• Reporting of undocumented accounts

Pre-validation environment and production timeline

The tax authorities also announced in a recent newsletter the implementation timetable for the new CRS reporting framework.

A dedicated pre-validation environment supporting CRS XML Schema Version 3.0 will become available on 12 October 2026.

The pre-validation environment will allow RFIs and service providers to test their reporting systems, XML generation processes and validation controls before the new reporting framework becomes mandatory on 1 January 2027. The current CRS XML Schema Version 2.0 format will no longer be accepted in that testing environment after 30 September 2026.

The tax authorities also indicated that the production environment for CRS XML Schema Version 3.0 filings is expected to become available on 25 January 2027, although this date remains subject to confirmation.

Next steps

Luxembourg reporting entities, fund administrators and reporting service providers should review the new User Manual and assess the impact of the transition to AEOI_LUX_V3.0 on their reporting infrastructure and governance processes.

Reporting entities should give particular attention to:

• Implementing the new schema
• Updating procedures and databases
• Training relevant teams
• Revising the record-of-steps documentation
• Reviewing and updating customer data amending notifications for reportable individuals
• Assessing whether their existing reporting solutions need to incorporate additional OECD reporting classifications, data fields or XML mappings to align with OECD CRS XML Schema Version 3.0 data requirements
• Reviewing correction workflows and reporting identifiers
• Reviewing the updated FAQ, including the treatment of undocumented accounts
• Testing their reporting systems through the dedicated pre-validation environment before the mandatory application date of 1 January 2027

Addressing these issues should help reporting entities complete necessary system changes and testing activities before the new framework becomes mandatory.