Quick summary
  • On 5 January 2026, the OECD released the ‘Side‑by‑Side’ package, introducing new and extended safe harbours for Pillar Two. 
  • The package simplifies compliance and clarifies how Pillar Two interacts with the US minimum tax system, especially for US-headed groups. 
  • From 2026, it offers streamlined ETR and top‑up tax mechanisms while leaving 2024–25 filing obligations unchanged.
On 5 January 2026, the Organisation of Economic Cooperation and Development (OECD)/G20 Inclusive Framework (the OECD) announced the ‘Side-by-Side’ administrative guidance package (SbS Package).

This introduces new safe harbours and extends existing safe harbours in a bid to reduce the compliance burden for Multinational Enterprises (MNE) that are in-scope of the Pillar Two rules. 

The Package introduces new safe harbours, extends transitional measures, and provides further guidance that will influence how multinational groups prepare for compliance from December 2026 onward.

The Package aims to streamline compliance, reduce duplication where domestic minimum tax regimes already apply and provide clarity regarding the interaction between Pillar Two and the United States minimum tax system. For many multinational groups – particularly those with United States head entities – this represents a meaningful shift in how top-up taxes will be assessed and allocated.

Key takeaways

The SbS Package delivers five key outcomes – here are the key takeaways: 

  • A series of simplification measures aimed at reducing compliance and reporting burdens for both MNEs and tax authorities when calculating effective tax rates (ETRs) and top‑up taxes under the GloBE rules.
  • Further alignment in the treatment of tax incentives globally, through the introduction of a targeted Substance‑Based Tax Incentive (SBTI) safe harbour.
  • New safe harbours for MNE groups with an ultimate parent entity (UPE) located in an eligible jurisdiction that meets minimum taxation requirements.
  • An evidence‑based stocktake process to ensure that the SbS framework maintains a level playing field for all Inclusive Framework members over time.
  • Reinforcement of the importance of Qualified Domestic Minimum Top-up Tax Returns (QDMTRs) as a key mechanism within the global minimum tax framework for safeguarding domestic tax bases. 
  • The changes will not impact filings in respect of the 2024 and 2025 income years and groups should continue to take steps to ensure they meet the 30 June 2026 filing deadline. 
  • Groups which qualify for the SbS safe harbour will still be required to file the GloBE Information Return (GIR) and QDMTR in jurisdictions which have implemented the rules.  

Background: why a ‘side‑by‑side’ solution?

The United States has not adopted the OECD’s Pillar Two rules in their standard form. Instead, it operates a set of domestic and worldwide minimum tax rules that the US considers to be broadly consistent with the Pillar Two policy intent. Together with its G7 allies, the US advocated for ‘side‑by‑side’ model, under which Pillar Two would operate in parallel with the US minimum tax regime, rather than displacing it.

Agreement on the SbS Package was reached in return for the US withdrawing its proposed retaliatory ‘revenge tax’, which would have imposed punitive measures on jurisdictions applying Pillar Two top‑up taxes to US‑headed groups. The result is a framework designed to reduce the risk of double taxation and excessive compliance costs, while maintaining the integrity of the global minimum tax system. 

The Package groups the items by the following areas: 

a. SbS Safe Harbour

The SbS safe harbour allows Constituent Entities (CEs) whose UPE is located in a jurisdiction with a sufficiently robust domestic and worldwide tax system (a Qualified SbS Regime), as listed on the OECD Central Record) to be exempt from the Income Inclusion Rule (IIR) and the Undertaxed Profits Rule (UTPR). Importantly, the QDMTR continues to apply in all jurisdictions that have implemented it.

Broadly, a jurisdiction will qualify as having a Qualified SbS Regime where it demonstrates:

  • a nominal corporate income tax rate of at least 20 per cent
  • a QDMTT or alternative minimum tax of at least 15 per cent
  • an eligible worldwide tax system applying to offshore income of foreign branches and controlled foreign companies (both active and passive)
  • mechanisms to address base erosions and profit shifting and
  • no material risk of an effective tax rate below 15 per cent on domestic or foreign profits.

Application of the SbS safe harbour is elective and must be made in the group’s GIR. It does not apply automatically.

The SbS safe harbour applies for income years commencing on or after 1 January 2026.

Grant Thornton comment: At present, only the United States is listed on the OECD Central Record as having a Qualified SbS Regime. As a result, for US‑headed groups, neither the IIR nor the UTPR will apply from income years commencing on or after 1 January 2026. 

b. UPE Safe Harbour

The UPE safe harbour applies where the UPE is located in a jurisdiction with a sufficiently robust domestic tax system (a Qualified UPE Regime), but that jurisdiction does not meet the additional worldwide tax system criteria required for the SbS safe harbour.

Under this safe harbour:

  • top‑up tax for all entities in the UPE jurisdiction is deemed to be nil for UTPR purposes only
  • other jurisdictions may still apply the IIR or UTPR to subsidiaries located outside the UPE jurisdiction
  • the UPE safe harbour replaces the transitional UTPR safe harbour, which expired on 31 December 2025.

The UPE safe harbour applies for income years commencing on or after 1 January 2026.

Grant Thornton comment: As at the date of release, no jurisdiction has yet been recognised as having a Qualified UPE Regime.

The SBTI safe harbour is designed to neutralise top‑up tax outcomes that would otherwise arise from certain Qualified Tax Incentives (QTIs), such as tax credits, super‑deductions, qualifying exemptions and preferential rates, subject to strict substance‑based caps.

Where an MNE group elects to apply the SBTI safe harbour:

  • QTIs are treated as an increase to the ETR numerator (adjusted covered taxes) based on their deemed tax value
  • QTIs are excluded from the ETR denominator, increasing the overall effective tax rate.

The uplift to the ETR numerator is capped at the greater of:

  • 5.5 per cent of eligible payroll costs or eligible tangible asset depreciation or
  • 1 per cent of the carrying value of eligible tangible assets.

The SBTI safe harbour applies for income years commencing on or after 1 January 2026.

Grant Thornton comment: While conceptually welcome, the SBTI safe harbour operates within a tightly defined and highly conditional framework. In practice, it is neither particularly generous nor simple to apply, and careful modelling will be required.

a. Simplified ETR Safe Harbour

The Simplified ETR safe harbour introduces a permanent, alternative method for determining whether a tested jurisdiction has top‑up tax exposure, provided that no top‑up tax arose in that jurisdiction in the preceding two years.

Key features include:

  • application on a tested jurisdiction basis, rather than entity‑by‑entity
  • top‑up tax is deemed to be zero where the simplified ETR is at least 15 per cent
  • calculations are based primarily on financial reporting data used in preparing the group’s consolidated financial statements.

Despite its name, the simplified ETR calculation still requires multiple adjustments, including basic, industry‑specific, conditional and optional adjustments and differs to the simplified ETR under the Transitional CbCR safe harbour. 

The Simplified ETR safe harbour generally applies for income years commencing on or after 1 January 2027, although limited early application from 1 January 2026 is possible.

Grant Thornton comment: The Simplified ETR safe harbour remains highly technical and data‑intensive. While it may reduce complexity relative to the full GloBE calculation, it still demands substantial systems readiness and data quality. 

b. Extension of the Transitional Country by Country Reporting (CbCR) safe harbour

The SbS Package extends the Transitional CbCR safe harbour by an additional year, from three years to four years.

  • The extension covers income years beginning on or before 31 December 2027 and ending on or before 30 June 2029.
  • The applicable safe harbour rate for the additional year remains 17 per cent.

Grant Thornton comment: This extension is a welcome development, giving MNEs additional time to enhance systems and processes required for full Pillar Two compliance.

The OECD stocktake and why it matters

The SbS Package introduces an evidence based stocktake that will periodically assess whether the safe harbours continue to operate consistently across jurisdictions. The stocktake will review whether jurisdictions listed as Qualified Regimes still meet the relevant criteria and whether the outcomes remain aligned with the intent of the global minimum tax.

Grant Thornton comment:

The stocktake reinforces that the safe harbours are not permanent. Jurisdictions may be added or removed over time, and multinational groups will need to monitor the OECD Central Record to ensure they are applying the correct treatment for each reporting year.

Australian implications

Amendments to the Australian domestic Pillar Two rules to reflect the SbS Package are expected in due course. However, Australian legislation already requires the Pillar Two rules to be interpreted consistently with OECD Administrative Guidance. 

The SbS Package does not apply retrospectively. Full Pillar Two compliance remains required for income years 2024 and 2025.

Importantly:

  • CEs remain subject to QDMTR even where the UPE qualifies for the SbS safe harbour
  • the SbS and UPE safe harbours do not remove Australian Pillar Two filing obligations
  • significant penalties may apply for non‑compliance, even where no top‑up tax ultimately arises.

While Australia and other jurisdictions may seek recognition as Qualified SbS or Qualified UPE regimes in the future, the registration and review process may be lengthy. Taxpayers should not rely on this outcome until formally confirmed in the OECD Central Record.

What MNE groups should do now

MNE groups should now:

  • assess whether they may be eligible for the SbS or UPE safe harbours from 1 January 2026
  • actively monitor the OECD Central Record, as eligibility depends entirely on whether the UPE jurisdiction is listed as having a Qualified SbS or UPE Regime
  • continue investing in systems and data capabilities to support the Simplified ETR safe harbour and broader Pillar Two compliance
  • review the availability and impact of QTIs to determine whether the SBTI safe harbour could mitigate incremental top‑up tax exposure.

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