Why trouble for the biggest foreign buyer of U.S. debt could ripple through America's bond market

Aggressive fiscal stimulus from Japan’s new prime minister Sanae Takaichi—including a ¥21.3 trillion supplementary package—has driven a sharp rise in long-dated JGB yields (10‑year above ~1.78%, 40‑year ~3.7%, 30‑year ~3.33%) and a weaker yen, evoking comparisons to the U.K.’s 2022 Truss episode; because Japan is the largest foreign holder of U.S. Treasuries (roughly 13%, about $1.19 trillion), higher domestic yields could prompt Japanese insurers, pension funds and other investors to keep more savings at home, reducing external demand for Treasurys and limiting how low U.S. long-term yields can fall. That dynamic would complicate U.S. efforts to lower borrowing costs and could mute market responses to Fed easing; however, spillovers have been limited so far—U.S. 2‑, 10‑ and 30‑year yields recently ticked down (to ~3.51%, ~4.06% and ~4.71% respectively) and Japanese buying of Treasuries continues due to yen depreciation—but the risk to global bond markets could play out over months or years, especially if Japanese yields and repatriation pressures persist.

Analysis

Japan’s new prime minister Sanae Takaichi approved a roughly 21.3 trillion yen supplementary stimulus package that has coincided with a sharp repricing of long-dated Japanese government bonds: the 10‑year JGB rose above ~1.78%, 30‑year JGB reached ~3.33% and the 40‑year touched ~3.7%, while the yen weakened to a 10‑month low. Markets are drawing parallels to the U.K. 2022 episode as higher domestic yields and a weaker currency raise questions about confidence in Japan’s fiscal path.

Japan is the largest foreign holder of U.S. Treasuries (about 13%, roughly $1.19 trillion as of September), so sustained JGB yield increases could incentivize repatriation of savings and reduce external demand for Treasurys, limiting how low U.S. long-term yields can move even if the Fed signals easing; Adam Turnquist and Marc Chandler highlighted the potential multi‑year impact and muting of typical catalysts that push Treasuries lower.

So far the spillover is limited: U.S. yields recently traded lower (2‑yr ~3.51%, 10‑yr ~4.06%, 30‑yr ~4.71%) and Japanese investors have continued to buy Treasuries amid yen depreciation, but weak JGB auction prints and the stimulus package elevate the risk that flows and yields could shift meaningfully over months to years.

Key Decisions for Investors

• Reassess duration exposure in U.S. Treasuries and consider trimming or hedging long‑duration positions given the risk that rising JGB yields could cap how low U.S. long rates fall
• Monitor JGB yield curves, the yen and monthly Japan Treasury holdings (Japan held ~$1.19 trillion in Treasurys as of September) as primary triggers for repatriation risk and shifting global bond demand
• Watch U.S. Treasury auction demand and Fed communications (term premium commentary and comments like John Williams’s) for signs that market expectations for cuts are being muted by overseas yield moves
• Consider FX‑hedged exposure or currency hedges for allocations sensitive to Japanese flows since yen weakness has supported outbound purchases but could reverse if domestic yields continue to rise
• Maintain liquidity and preparedness to add risk selectively on dislocations if repatriation pressures or a repricing in global yields produce attractive entry points