Pillar Two has always been more than a new calculation. It is a global compliance framework being implemented simultaneously across multiple jurisdictions, each with its own legislation, administrative processes and filing requirements.
The latest implementation package from the OECD reinforces that reality.
Published on 11 September 2026, the package introduces three important developments: a framework for reviewing countries’ domestic Pillar Two legislation, an updated GloBE Information Return (GIR) and further Administrative Guidance.
Individually, each development is significant. Together, they signal a wider shift in the Pillar Two journey.
The framework is moving beyond implementation and into a period of active administration, review and refinement. For multinational groups, the question is no longer simply whether they can complete a Pillar Two filing. It is whether their compliance process can continue to adapt as the rules, reporting formats and jurisdictional requirements evolve.
Consistency is becoming a formal part of implementation
One of the most important elements of the package is the introduction of a full legislative review process.
Inclusive Framework members will use this process to assess whether domestic rules implementing the Global Minimum Tax remain consistent with the GloBE Model Rules and Commentary. Where inconsistencies are identified, the Inclusive Framework may issue recommendations to help jurisdictions address them.
This is intended to support more consistent outcomes, improve tax certainty and reduce the compliance burden created by divergent domestic rules.
However, consistency will not arrive overnight.
Jurisdictions have implemented Pillar Two at different speeds and through different legislative frameworks. Their rules will now be subject to more detailed examination and, in some cases, may need to be amended following that review.
For multinational groups, this creates an important distinction between monitoring whether a jurisdiction has implemented Pillar Two and understanding exactly how its rules operate at a particular point in time.
A static jurisdictional checklist will not be enough. Tax teams need to monitor changes to domestic legislation, understand which version of the rules applies to each reporting period and retain a clear record of how filing positions were reached.
The review process should ultimately create greater alignment. In the short term, however, it reinforces the need for ongoing jurisdictional monitoring and strong version control.
The GIR is changing for the next filing cycle
The OECD has also published an updated GloBE Information Return, incorporating the simplifications introduced through the Side-by-Side package agreed in January 2026.
The revised GIR applies to fiscal years commencing on or after 31 December 2025. It includes reporting fields and explanatory guidance covering measures such as the Side-by-Side Safe Harbour, Simplified ETR Safe Harbour and Substance-based Tax Incentive Safe Harbour.
A revised XML Schema is now being developed to reflect these changes.
This is not simply a technical update for software providers or IT teams. It has direct consequences for the entire compliance process.
Data requirements may change. Existing reporting mappings will need to be reviewed. Validation rules, workflows and filing outputs may need to be updated. The OECD has also indicated that the new schema will be introduced through a defined cut-off date, with different schema versions applying depending on the reporting period and filing date – including potentially for amendments and corrections.
Groups therefore cannot assume that the process used for their first GIR can simply be repeated next year.
The underlying data may remain familiar, but the way it must be structured, validated and submitted is evolving.
Simplification does not mean standing still
The Side-by-Side package was designed to simplify aspects of Pillar Two and provide greater certainty for multinational groups.
But simplification should not be confused with stability.
Every new safe harbour or reporting simplification introduces its own eligibility conditions, elections, data requirements and documentation expectations. Groups must still be able to demonstrate why a particular treatment applies and retain the evidence supporting that conclusion.
The updated GIR illustrates this clearly. Some groups may benefit from reduced calculation or reporting requirements, but they must first identify the appropriate safe harbour, confirm that its conditions are satisfied and supply the relevant information through the return.
The operational challenge is therefore changing rather than disappearing.
The most effective Pillar Two processes will be those that can accommodate simplifications without losing control, consistency or auditability.
Technical guidance highlights the importance of data context
The latest Administrative Guidance addresses two specific issues.
First, taxes that apply explicitly because a taxpayer is subject to an Income Inclusion Rule or Undertaxed Profits Rule in another jurisdiction are classified as “Explicitly Conditional Taxes”. These taxes are not treated as Covered Taxes for GloBE purposes.
Further guidance on other potentially discriminatory tax features is expected before the end of 2026.
Second, the OECD has clarified that the QDMTT Safe Harbour can continue to apply where a QDMTT is calculated using local financial accounting standards and the required local accounting period does not align with the Ultimate Parent Entity’s fiscal year, provided the relevant conditions are met.
Although both points are technical, they demonstrate a broader operational principle.
Pillar Two data cannot be understood through values alone. Tax teams also need context: what triggered a tax, which accounting standard was used, which reporting period the information relates to and how that information connects to the wider group calculation.
A system that records only the final tax amount will struggle to support that level of analysis. Effective compliance requires traceable source data, clearly documented adjustments and the ability to apply different treatments across jurisdictions and reporting periods.
What should multinational groups do now?
The latest package should prompt tax teams to review the assumptions underpinning their next compliance cycle.
Priorities should include:
- Assessing the revised GIR requirements to identify changes to data points, elections, safe harbour reporting and explanatory information.
- Reviewing existing data mappings to determine whether current finance, tax and consolidation systems capture the information required by the updated return.
- Preparing for the revised XML Schema by ensuring filing processes can accommodate new formats and validation rules when they are released.
- Strengthening jurisdictional monitoring so changes resulting from the legislative review process can be identified and reflected promptly.
- Maintaining clear rule and data lineage to show which legislation, guidance, elections and source information supported each filing position.
- Testing the full process early, from data collection and calculation through to review, validation and submission.
This should not be treated as a one-off remediation exercise. Pillar Two processes need to be designed around continuing change.
A successful first filing is a baseline, not a blueprint
The first Pillar Two compliance cycle gave organisations an opportunity to establish processes, identify data gaps and understand where manual effort or external support was required.
The OECD’s latest package makes clear that the next cycle will not simply be a repeat of the first.
Reporting structures are changing. Domestic legislation will face further scrutiny. New guidance will continue to refine how individual taxes, accounting standards and safe harbours interact with the GloBE framework.
The strongest tax functions will use the experience of their first filing as a foundation while retaining the flexibility to respond to what comes next.
That means moving beyond spreadsheets, fixed templates and deadline-led projects towards a controlled, repeatable compliance model. Data, calculations, jurisdictional requirements, filing outputs and supporting evidence need to remain connected as the rules evolve.
In the next phase of Pillar Two, accuracy remains essential. But accuracy at a single point in time is no longer enough.
The real measure of readiness is whether an organisation can adapt without rebuilding its compliance process every time the framework changes.
Alphatax Pillar Two helps multinational groups manage calculations, data, safe harbours and filing requirements through a connected, auditable process. Discover more about how technology can support a more adaptable approach to Pillar Two compliance.