Inflation, Interest Rates, and AI—How the OECD's Global Economic Outlook Has Changed in Nine Months

Key Takeaways

The points that have remained unchanged in the OECD Economic Outlook reports from December 2025 to September 2026 are summarized below. This article focuses on the items that have changed.

In Short

Comparing the four OECD Economic Outlook reports from December 2025 to September 2026, the global GDP growth forecasts have remained almost unchanged. However, the underlying assumptions for the global economy have shifted significantly. Inflation has moved from the ‘convergence’ mode seen in December 2025 to a ‘cautionary’ mode, with the September 2026 report recognizing its ‘stickiness.’ Consequently, monetary policy is now expected to feature higher interest rates for longer. The positioning of AI has also changed from a primary driver of growth to a risk factor involving massive capital procurement and power constraints. Moving forward, trends in long-term interest rates, energy reserves, AI investment, and food prices will be critical.

In Detail

1. While global GDP growth forecasts have not changed significantly, the OECD’s perspective has.

The OECD updates its global economic outlook quarterly. So, what exactly has changed when comparing the December 2025 outlook with the September 2026 outlook? The first thing that catches the eye is the global GDP growth forecast. The forecast for 2026 was maintained at 2.9%, and the forecast for 2027 was only slightly revised downward from 3.1% to 3.0%. Looking at global GDP alone, not much has changed over the past nine months. However, the underlying content is quite different. The factors driving the economy have changed fundamentally, including the resurgence of energy prices due to heightened tensions in the Middle East, the sharpest rise in long-term interest rates in 15 years, and the rapid expansion of AI investment and massive capital raising that strongly supports the global economy.

2. The biggest change was in ‘inflation’.

In this revision of the OECD outlook, the most significant change is the perception of inflation. In the December 2025 forecast, G20 inflation was expected to converge steadily to 2.8% in 2026 and 2.5% in 2027. However, the outlook shifted to a cautionary mode from 2026 onwards, and in the September 2026 report, this was significantly revised upward to 4.1% for 2026 and 3.6% for 2027. What is essential here is that this is not a superficial change where figures were simply rewritten due to rising crude oil prices. The OECD’s own perspective has fundamentally shifted from viewing ‘high prices as temporary and converging to target levels’ to recognizing that ‘inflation is becoming sticky and prolonged through complex effects.’ Behind this lies a clear causal relationship. Disruptions in energy supply due to the situation in the Middle East, combined with bottlenecks in refining capacity, caused fuel prices such as gasoline and diesel to soar. Furthermore, this spilled over into food prices due to fertilizer shortages and abnormal weather, directly pushing up inflation expectations for households and businesses. This shift toward a structure where inflation is prolonged and remains high, rather than just a simple rise in resource prices, is the most significant implication of this revision.

3. As a result, the assumptions for monetary policy have also changed.

The deterioration in the inflation outlook has fundamentally rewritten the assumptions for central bank monetary policy. As of December 2025, a full-scale interest rate cut cycle and an accommodative financial environment were expected against the backdrop of steady price deceleration. However, when concerns about a resurgence of inflation emerged sharply in March 2026, a stance of holding policy rates steady and maintaining caution became entrenched by June. By the September report, the situation had developed to the point where about one-third of central banks in G20 countries were implementing interest rate hikes (tightening). This sudden change in inflation expectations hit the steering of monetary policy directly. In addition to the rise in short-term interest rates guided by central banks, the fact that long-term government bond yields in major countries have reached their highest levels in 15 years—driven by fiscal concerns and massive corporate bond issuance by AI companies—is making the situation more serious. It is not just the rise in short-term rates, but this persistence of high long-term interest rates that constitutes a new structural risk facing the global economy.

4. Another change is the positioning of ‘AI’.

Another interesting change in perception in the global economic outlook is the positioning of AI. In the December 2025 report, AI-related investment was evaluated positively as a ‘driver of growth’ that strongly supports corporate capital investment, trade in high-tech products, and ultimately the growth of the global economy as a whole. However, the September 2026 report shifted to a multifaceted view that, while acknowledging the positive aspects supporting growth, also looks at the associated risks. Specifically, the impact on the bond market is beginning to be recognized, with active corporate bond issuance by AI companies mentioned as a factor contributing to the rise in long-term interest rates. Furthermore, constraints (bottlenecks) in power supply due to the rapid increase in data centers and the procurement of advanced semiconductors were pointed out as risks that could delay the monetization of AI investments. Thus, the report has revised its perception (or ‘updated its take’) on AI, viewing it not just as a ‘factor that boosts growth,’ but as an ‘entity that can also become a risk to financial markets through capital procurement and infrastructure constraints while simultaneously supporting growth.’

5. Trade policy can no longer be read by ‘tariff rates’ alone.

The U.S. average effective tariff rate moved from 14.0% (December 2025) to 9.9% (March 2026), 9.6% (June 2026), and then to 10.9% (September 2026). If you only follow the numbers, it looks like ‘tariff rates are repeatedly rising and falling.’ However, the important change in perception this time is that the true impact of trade policy can no longer be captured by a single average tariff rate alone. The impact of trade policy can no longer be measured by the ‘average tariff rate figure’ alone. Due to the proliferation of individual tariffs and frequent institutional changes, the real issue has shifted to ‘policy unpredictability’ and ‘damage to supply chains.’ The raising of trade barriers and sudden changes are forcing companies to restructure their supply chains, becoming the biggest factor leading to structural cost increases.

6. Six variables that should be continuously monitored.

Based on the above understanding, we have summarized the elements that the OECD identifies as needing continuous monitoring.

In English

While headline global GDP projections across the four OECD reports from December 2025 to September 2026 are virtually unchanged, the underlying macro narrative has fundamentally shifted. First, inflation has evolved from an expected convergence to a persistent ‘sticky’ reality, cementing a higher-for-longer rate outlook. Second, AI has been re-rated from a pure secular growth driver to a multi-faceted risk factor constrained by heavy capex pressures and power bottlenecks. Going forward, our focus must remain squarely on long-term yields, energy reserves, AI capex sustainability, and food price dynamics.

Personal Opinion

There are many requirements, as listed below, for properly managing the current global economy. It seems likely that this period of uncertainty will continue for some time.

• Stabilization of the Strait of Hormuz

• Ensuring the benefits of AI spread widely to non-AI-related industries and beyond

• Timely and appropriate implementation of monetary tightening

• Proper control of fiscal debt