- “What we call beginning is often the end. And to make an end is to make a beginning. The end is where we start from.” T.S. Eliot.
As readers may remember, in my October 2025 article[i], I examined the emerging Side-by-Side (SbS) solution at a time when the discussion was still unfolding as a political negotiation rather than a settled legal doctrine. January 2026 now marks the turning point where that uncertainty gave way to institutional clarity.
On 5 January 2026, the OECD Inclusive Framework released the long-anticipated Side-by-Side package, formally establishing the framework that clarifies how the Pillar Two Global Anti-Base Erosion (GloBE) rules apply to U.S. multinational groups through a new safe harbor recognizing the U.S. tax system as compliant, while also introducing several complementary simplification measures.
To recall the context, the June 2025 G7 understanding had first raised the possibility that the United States could operate alongside the GloBE system without formally enacting its rules. Yet at that stage the concept remained largely theoretical: no formal eligibility criteria had been defined, no election mechanics had been articulated, and no systemic safeguards had yet been introduced. The language circulating at the time “carve-out,” “exemption,” or “special treatment” captured precisely the uncertainty surrounding how such coexistence might ultimately be structured.
The risk, as many observers perceived it, was that granting relief to the largest economy in the world might dilute the coherence of the global minimum tax project. Would the Side‑by‑Side approach weaken the enforcement pyramid built around the Income Inclusion Rule (IIR), the Undertaxed Profits Rule (UTPR), and Qualified Domestic Minimum Top‑Up Taxes (QDMTTs)?
Yet the fall 2025 hearing and debate obscured a deeper institutional question. The United States is not a low‑tax jurisdiction resisting minimum taxation. It operates a 21% federal corporate income tax, sub‑national taxation, a Corporate Alternative Minimum Tax (CAMT), Subpart F inclusions, and Net CFC Tested Income rules. The tension was not about under‑taxation; it was about duplication and competitive distortion.
The negotiation phase therefore exposed two competing visions of international tax governance. One insisted on legislative symmetry, the idea that legitimacy required formal replication of the GloBE Model Rules. The other suggested that functional equivalence, where domestic systems already achieve minimum tax outcomes, could be recognized without undermining the global framework. As of fall 2025, that second vision remained untested.
January 2026: Codifying Equivalence Through the Side‑by‑Side Safe Harbor
On 5 January 2026, the OECD’s administrative guidance transformed the Side‑by‑Side concept into structured institutional architecture. The United States was formally listed in the OECD Central Record as possessing a ‘Qualified Side‑by‑Side Regime.’ The framing shifted decisively: from political accommodation to codified equivalence.
Under the SbS Safe Harbor, multinational enterprise (MNE) groups whose Ultimate Parent Entity (UPE) is located in a qualified jurisdiction may elect to deem top‑up tax under the IIR and UTPR to zero for fiscal years beginning on or after 1 January 2026. This relief is not absolute. QDMTTs remain fully applicable, and GloBE Information Return (GIR) obligations continue. The enforcement structure is recalibrated not dismantled.
Crucially, the eligibility criteria for a Qualified SbS Regime are substantive. They require an eligible domestic tax system, including a sufficiently robust statutory corporate tax rate and a financial‑statement‑based minimum tax of at least 15%, as well as an eligible worldwide tax regime capable of capturing foreign income without material risk of sub‑minimum effective taxation. In other words, equivalence must be demonstrated — not presumed.
Equally significant was the decision to deny retroactive application. Fiscal years 2024 and 2025 remain governed by the original GloBE framework. This preserved legal certainty and avoided the perception that the OECD was rewriting the rules mid‑cycle. Compromise was prospective, reinforcing institutional credibility.
The January package also addressed transitional integrity concerns. Allocation safeguards were clarified to prevent UTPR windfalls in jurisdictions that might delay implementation of the SbS framework. Additional mechanisms — including a UPE Safe Harbor and a Substance‑Based Tax Incentive Safe Harbor — further demonstrated that the reform was systemic rather than U.S.‑specific.
From Negotiation Narrative to Strategic Governance
The difference between fall 2025 and January 2026 administrative guidance is therefore structural. What began as a negotiation instrument became a clear framework of coordinated equivalence.
| September 2025 – Negotiation Phase | January 2026 – Codified Framework | Strategic Consequence |
| Political carve‑out rhetoric | Formal Qualified SbS Regime recognition | Shifts from exemption narrative to principled equivalence |
| Uncertain mechanics | Defined eligibility criteria and election process | Establishes legal certainty |
| Retroactivity debated | Prospective application only | Protects rule‑of‑law continuity |
| UTPR allocation concerns | Allocation safeguards clarified | Preserves competitive neutrality |
| Perception of weakening framework | Integration within GloBE commentary | Strengthens institutional durability |
Strategically, the Side‑by‑Side rules signal an evolution in international tax governance. They recognize that minimum taxation outcomes can be achieved through different legislative architectures. By anchoring relief in demonstrable equivalence rather than political exception, the OECD reframed the debate.
This reframing is decisive. A system that insists on mechanical uniformity risks geopolitical rupture. A system that accepts coordinated pluralism — while preserving minimum effective tax outcomes — strengthens its legitimacy. The Side‑by‑Side regime therefore represents not dilution, but maturation.
In my October 2025 article, the Side‑by‑Side concept was still a negotiation hypothesis. By January 2026, it had become institutional design. That transition from political bargaining to codified equivalence may ultimately prove to be a significant development in the post‑BEPS era.
The Side‑by‑Side rules demonstrate that global coordination does not require rigid uniformity. It requires shared outcomes, transparent criteria, and adaptive architecture.
If September 2025 revealed the fragility of narrative, January 2026 confirmed the resilience of design.
Yet behind this sophisticated architecture lies a simpler reality: for taxpayers and MNEs the true challenge may ultimately be the ever-growing weight of navigating its expanding web of compliance.
Cheers!
The opinion expressed in this article is exclusively that of the author and does not reflect and cannot be related to her professional environment.
[i] EU Signals “Side-by-Side” Pillar 2 Carve-Out: Can the U.S. Be Exempted? https://www.legaltoday.com/colaboradores/b/eu-signals-side-by-side-pillar-2-carve-out-can-the-u-s-be-exempted-2025-10-16/
