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Circular CSSF 26/911: Luxembourg Money Market Funds, MMFR Stress Tests, and the 2026 Reporting Date
Luxembourg money market funds need to separate three moving pieces: the MMFR liquidity and stress-testing rulebook, CSSF circular updates that apply ESMA scenarios, and the 2026 policy debate on liquidity guidance. Circular CSSF 26/911 updates the local reference point for ESMA 2025 stress-test scenarios, while CSSF and EU consultation work on weekly liquid assets and liquidity fees should be monitored as a separate forward-looking policy track.
On May 19, 2026, the CSSF published Circular CSSF 26/911. The circular concerns ESMA guidelines on stress test scenarios under Article 28 of Regulation (EU) 2017/1131 on money market funds. The CSSF page states that the circular updates the 2025 ESMA stress-test scenario guidance and replaces Circular CSSF 25/877.
Direct Answer
For an MMF manager, the immediate control task is to confirm which fund compartments are in scope, update references from superseded circulars where relevant, evidence Article 28 stress-test assumptions, check Article 37 MMFR reporting production, and brief governance bodies on any methodology or liquidity-tool changes. Do not treat the June 2026 consultation on MMF liquidity guidance as already-final law; track it, record the exposure assessment, and rely on current CSSF, ESMA, and EU texts for filings and investor disclosures.
Quick scan
- Check whether the fund is an MMF under Regulation (EU) 2017/1131.
- Verify that internal references now cite Circular CSSF 26/911 instead of Circular CSSF 25/877.
- Review whether the June 30, 2026 reporting implication affects calendars, templates or ownership.
- Keep the official CSSF circular and the referenced ESMA materials as the live technical source.
- Escalate if reporting teams still rely on stale scenario assumptions or unclear ownership.
| Reader question | Practical answer |
|---|---|
| Does this apply to every Luxembourg fund? | No. The source is about money market funds under the MMF Regulation stress-test framework. |
| Is Circular CSSF 25/877 still the current circular? | No. The CSSF source says Circular CSSF 26/911 replaces Circular CSSF 25/877. |
| Is this an investor recommendation? | No. It is a regulatory reporting and stress-test source, not a signal to buy, sell, or hold a fund. |
| What should operations teams do? | Confirm reporting templates, scenario data, governance ownership, and deadline readiness against the official source. |
Key Dates
| Date | Event |
|---|---|
| May 19, 2026 | CSSF published Circular CSSF 26/911. |
| June 30, 2026 | CSSF source identifies reporting implications from this date. |
| June 2, 2026 | This article checked the official CSSF source. |
Who Is Affected
The primary audience is Luxembourg money market funds, their management companies or AIFMs where relevant, risk-management teams, compliance officers, fund boards, depositaries, administrators, auditors, and service providers that support MMF reporting or stress-test processes.
Retail and professional investors may still benefit from the article, but the user task is different. An investor should understand that stress testing is part of the regulatory and risk-management framework. The investor should not infer fund quality or suitability from the existence of a circular alone.
What Changed
The CSSF source identifies Circular CSSF 26/911 as replacing Circular CSSF 25/877. Editorially, that means pages and checklists that cite Circular CSSF 25/877 as current need an update. Operationally, teams should verify whether their 2026 reporting calendar, stress-test assumptions, system templates, and review process reflect the 2025 ESMA update referenced by the CSSF.
This article intentionally does not reproduce the technical scenario values. MMF reporting teams should use the official CSSF circular and the ESMA materials it references for the live technical basis.
Practical Checklist
| Check | Why it matters |
|---|---|
| Identify whether the fund is an MMF under Regulation (EU) 2017/1131. | The circular is tied to the MMF stress-test framework. |
| Replace stale references to Circular CSSF 25/877. | CSSF 26/911 is the current replacement source. |
| Confirm the June 30, 2026 reporting implication. | The date affects reporting readiness and internal calendars. |
| Map responsibility across risk, compliance, fund administration, and board reporting. | Stress-test reporting can fail when ownership is unclear. |
| Keep investor-facing explanations separate from regulatory operations. | Investors need plain-language risk context, not operational templates. |
Next-step checklist
- Gather the current MMF scope list, reporting calendar and template set for all affected funds.
- Check every current policy, checklist and operations note for stale references to Circular CSSF 25/877.
- Verify who owns scenario updates, XML or reporting templates, board reporting and sign-off before June 30, 2026.
- Save the official CSSF circular, the referenced ESMA materials and internal readiness evidence in one archive.
- Stop using a reporting template if the scenario basis or circular reference has not been refreshed.
- Escalate any mismatch between fund scope, reporting ownership and the official source timetable.
How This Fits the CSSF Fund Framework
Money market funds sit inside the broader Luxembourg investment-fund ecosystem, but they have specific EU MMF Regulation obligations. For broader source navigation, see CSSF investment fund regulatory framework in Luxembourg and Luxembourg CSSF rules tracker.
Official Source Check
This guide was checked on June 4, 2026 against the official source URLs listed in this article. Recheck CSSF, ESMA, and EU materials before relying on stress-test scenarios, reporting calendars, or pending MMF liquidity guidance.
Official Sources
- CSSF: Circular CSSF 26/911
- CSSF: Circular CSSF 25/877
- CSSF: Investment fund industry regulatory framework
- EUR-Lex: Regulation (EU) 2017/1131 on money market funds
Bottom Line
Circular CSSF 26/911 is a current-source update for Luxembourg MMF stress-test coverage. The essential reader message is specific: use CSSF 26/911 instead of CSSF 25/877 for the current circular reference, and verify reporting readiness for the June 30, 2026 implications through the official source.