GMT, GIR, and Beyond: Tax Strategies for the Road Ahead

We recently spoke with CSC Corptax international tax experts Gary Colbert and Ken Siegel about the Global Minimum Tax (GMT), the GloBE Information Return (GIR), and what lies ahead for customers. Ken, Director of Services, and Gary, Senior Director of Services, share key updates for managing Pillar Two, along with insights into how Corptax supports the process.

Ken, can you update us on important recent developments and walk us through a timeline of what to expect, short- and long-term?

Ken Siegel: Sure. The Organization for Economic Co-operation and Development (OECD) recently opened a comment period on the GloBE Information Return. Comments focused on the need for simplification and standardization. In addition, many respondents pushed for a universal schema and a common system for sharing GIRs across Pillar Two countries to streamline the process by eliminating local variations. We’ll see how the OECD responds to the feedback.

Meanwhile, the EU has proposed a system for MNEs to file one Top-up tax return for the entire EU, which aligns with the OECD’s simplification efforts. As the OECD refines the GIR, the EU’s proposal will include those modifications in the EU filings.

More jurisdictions are rolling out Pillar Two legislation, while others, like Belgium, are implementing notification requirements. Belgium’s detailed early demands have sparked criticism, prompting other countries to consider simplifying their notification filing requirements. So, the global effort to bring more clarity and efficiency to international tax compliance is underway.

With more countries adopting Pillar Two rules and with the growing resistance to notification requirements, how does the US fit in?

Ken Siegel: The US hasn’t adopted Pillar Two and isn’t likely to any time soon. However, there are potential revenue implications. If other countries impose a Top-up tax under the Undertaxed Profit Rule (UTPR), some revenue could shift away from the US. That said, UTPR rules for US-parented multinational groups won’t take effect until 2026, thanks to the UTPR Safe Harbor provision. So, for now, it’s a waiting game to see how things wind up on this front.

With many Pillar Two changes happening, how does Corptax help clients navigate them?

Ken Siegel: We proactively monitor and anticipate changes to help our clients stay ahead. For example, a few years ago, we launched a GMT international tax planning and compliance tool to identify where a Top-up tax might apply once the rules went live in 2024. Since then, we’ve expanded it to cover what we like to call ‘all things GMT.’

Our focus has been on delivering detailed calculations that align with the OECD’s evolving model rules. Clients use the system to calculate GloBE income and covered taxes with trial balance data, flag GloBE income and tax adjustments, and leverage BEPS CbC data for Safe Harbor calculations. They can also use international data for GILTI tax allocations. It’s a comprehensive and powerful solution.

Ownership data is another critical component as it helps to determine where a Top-up tax needs to be paid under an Income Inclusion Rule (IIR) and UTPR. To keep clients informed, we built a legislation tracker directly into Corptax. This tracker is updated as jurisdictions adopt rules like IIR, UTPR, or QDMTT, enabling clients to run what-if scenarios and plan with confidence.

What should tax teams expect from the timeline going forward?

Ken Siegel: Tax teams should expect the real compliance work to kick in during 2025, covering 2024 obligations. This includes notifications, local QDMTT filings, and the GIR. The first GIR filing deadline is 18 months after year-end, so it’s due in late June 2026 for calendar year taxpayers. The IIR rules take effect in 2024, while the UTPR generally starts in 2025. In a nutshell, it’s happening.

To help our clients navigate these requirements. we’ve developed international tax planning reports that align with the GIR schedules. These reports will enable clients to generate the XML files needed for GIR filing seamlessly. We closely monitor OECD updates and adjust our tools accordingly. We also support data collection and jurisdiction-specific notifications—including for Belgium—integrating new details as they become available.

Gary, how has the GMT solution evolved since it started as an international tax planning tool in 2021? And what’s the roadmap for 2025 and beyond?

Gary Colbert: The Corptax GMT solution has been—and continues to be—a true success story. Because we acted so early, we were able to continually enhance the product as requirements evolved and give our customers what they needed when they needed it. When the OECD released the model rules in 2021, we identified an immediate need for risk assessment. In early 2022, we launched Corptax GMT’s first version which included a tool for calculating ETRs by jurisdiction. This let clients quickly identify areas of exposure.

We’ve rapidly advanced from there. As the market moved beyond initial risk assessments to needing more detailed planning capabilities, we expanded Corptax GMT to model Top-up taxes, IIRs, and UTPRs. This gave organizations a way to analyze, predict, and generate sharable insights.

By 2024, as components of Pillar Two became effective in some jurisdictions, the focus shifted from planning to operations. With IIRs and QDMTTs becoming effective, Corptax GMT grew to become a real-time operational tool—automating IIR and UTPR allocations and integrating data with provision processes, for example.

Looking ahead to 2025, Corptax GMT will hone in on compliance with even more precision. We’re building GIR reports and aligning with the OECD’s final schema to generate the necessary XML files. We’re also adapting Corptax GMT to handle local compliance rules, and we’re developing data sources for countries like Belgium, which has detailed notification requirements.

Further, we’re enhancing Corptax GMT’s performance for global users—making sure it works for teams that don’t access Corptax daily. It’s very satisfying to see Corptax GMT becoming our clients’ go-to tool for Pillar Two compliance.

How are organizations approaching Safe Harbors in 2024? What’s the general sentiment in the market?

Gary Colbert: The approach varies depending on where organizations are in their Pillar Two process. In 2022 and 2023, many companies were trying to understand what Pillar Two meant for them. By 2024, a lot were leaning into transitional Safe Harbors and deciding to delay more complex compliance for a year or two.

However, as we enter 2025, that mindset is shifting. Safe Harbors are temporary, and companies are beginning to take the process much more seriously. Even under a Safe Harbor, the GIR reporting requirement still applies—companies must gather data and report their status. While Safe Harbors gave businesses some breathing room, companies realize it’s time to prepare for compliance.

With the GIR deadline pushed to 2026, what’s your advice to tax teams to avoid a mad dash in 2026 to figure out 2024 data?

Gary Colbert: Start building your process now. The GIR requires a huge volume of data. Even if the OECD addresses the public comments by simplifying a final version, it’s still going to be a heavy lift. Make sure you have a system in place to organize and report the data consistently, no matter where it’s being filed.

You’ve written about the intersection of data, people, and technology in The Pillar Two Playbook. How do these elements work together, and why is technology so critical moving forward?

Gary Colbert: Technology is the glue that holds everything together. The complexity and volume of data required for Pillar Two make it nearly impossible to manage without the right systems in place. Tax Operations needs a way to securely centralize, standardize, use, review, and report on data across jurisdictions.

They also need a way to collaborate, which is crucial for global calculations. By centralizing the process in one tool, everyone stays aligned—a must as we approach 2025 and 2026 compliance deadlines.

Just 10 or 15 years ago, tax processes were more siloed. Now, with international tax reform, there’s a shift toward collaboration among countries. How does this affect multinational companies?

Gary Colbert: We’re witnessing this global shift in real time; 2025 will see many more companies reevaluating their systems and processes to adapt. Like BEPS Country-by-Country reporting, Pillar Two introduces global reporting requirements with local filing obligations, demanding consistency across jurisdictions and coordination at HQ. Global collaboration is essential, with tax technology playing a critical role in streamlining efforts. By adopting the right tools and strategies, companies can simplify complex workflows and stay ahead as requirements evolve. This approach not only ensures compliance but also creates opportunities to drive efficiencies and foster stronger collaboration across global operations.