Last updated
CSSF U1.1 Reporting New Format, eDesk and S3: Practical 2026 Submission Guide
The CSSF announced on 5 January 2026 that U1.1 reporting evolved from 1 January 2026 with a new format applicable to reference dates from December 2025 onwards. Reporting teams should treat this as a format, channel, delegation and evidence-control change, not only as a template refresh.
Direct answer
For U1.1 reference dates from December 2025 onwards, confirm that the file is built in the new U1.1 format and submitted through one of the CSSF-supported methods: the dedicated eDesk procedure or an API solution based on XML reports submitted via the S3 protocol. The CSSF says the new format includes additional features designed to improve transmission and management of reports, including delegation, and that the detailed user guide is available inside the eDesk procedure.
Readiness matrix
| Control area | What changed or must be confirmed | Evidence to keep |
|---|---|---|
| Reference-date scope | New format applies to reference dates from December 2025 onwards. | Reporting calendar, reference-date list and source note from CSSF communique. |
| Submission channel | Use either the dedicated eDesk procedure or XML submission through the S3 API route. | Channel decision, access proof, test result and submission receipt. |
| Delegation | Check who can prepare, validate and submit the report, especially where a service provider is involved. | Delegation mandate, user roles, maker-checker record and approval log. |
| Format validation | Confirm that the output follows the current U1.1 structure before submission. | XSD or schema validation result, error log, fix owner and final accepted file. |
| Operational fallback | Prepare a route for portal access, S3 failure, rejected XML, missing delegation or late corrections. | Escalation contacts, incident note, resubmission plan and CSSF correspondence. |
Practical filing workflow
- Identify all entities, reference dates and internal owners affected by the December 2025 onwards format.
- Choose the submission route stated by the CSSF: the dedicated eDesk procedure or the S3 XML API where the reporting operating model supports it.
- Review the eDesk user guide and any internal procedure updates before the first live filing.
- Test file generation and validation before the statutory or supervisory deadline, not on submission day.
- Record who reviewed the data, who approved the file, who submitted it and what receipt or rejection message was returned.
What management should ask
Management does not need to inspect every XML field, but it should know whether the first new-format filing has an owner, a tested channel, a delegated-submission control, a validation log and a fallback. Where a group service provider or administrator handles filing, the regulated entity should still keep evidence that the provider is using the correct format and that exceptions are escalated quickly.
Official sources
- CSSF: U1.1 Reporting - New format and new features, communique published 5 January 2026.
- CSSF eDesk, the portal entry point for eDesk procedures.
- CSSF file transport and data protection, source context for secure transmission and reporting channels.
Bottom line
The U1.1 change is live for December 2025 reference dates and later. A defensible 2026 filing pack should show the applicable reference date, the selected channel, the delegated roles, the validation result, the submission receipt and the route for correcting a rejected report.