Stress-Testing the ECB’s Reaction Function: When the Long End Tightens First

The ECB Reaction Function

Official data. The Governing Council raised the deposit rate to 2.50% on 10 September, after a 25bp hike on 11 June and a hold in July. Staff project headline inflation at 3.0% in 2026, 2.5% in 2027 and 2.1% in 2028, core at 2.5%, 2.6% and 2.3%, and growth at 0.9%, 1.4% and 1.5%. On 28 September President Lagarde restated the logic: the ECB does not react to energy prices as such, but to the risk that they become embedded, judged through three criteria — the inflation outlook, underlying inflation dynamics, and the transmission of policy to borrowing costs and growth. Her verdict was higher inflation ahead but no sign yet of embedding or of wage pass-through; a shock that is “too large to look through” but warrants only a measured response.

Official data. Her key addition concerned the third criterion. Since the September meeting, long-term yields have climbed sharply, which she said will slow growth and dampen pass-through by more than the staff baseline assumed.

Market pricing and external analysis. Markets listened. After the flash print, pricing for an October hike fell to roughly 20% (Danske Bank), from around 50% earlier in the month (MUFG). MUFG dropped its October-hike call, now expects the next hike in December, and judged that three to four further hikes had been over-priced. Isabel Schnabel, an outspoken hawk, said on 30 September that policy can tolerate a more gradual return to target if expectations stay anchored and that the global yield rise may weigh on growth more than assumed, while noting that robust credit growth suggests financial conditions are not yet restrictive (Reuters). Joachim Nagel said on 1 October that the Transmission Protection Instrument (TPI) is about price stability, not spread levels (Reuters).

LBMR interpretation. Three features define the function today. First, an asymmetric burden of proof: because the long end already tightens, a further hike needs evidence of second-round effects, not merely a hot headline. Second, the substitution is imperfect. The September move was a term-premium and sovereign-risk move, not a re-pricing of the policy path: on 2 October the Bund yield fell towards 3.4–3.5% while the OAT stayed near 4.94%. It tightens financing conditions without signalling resolve to wage-setters or re-anchoring expectations. Third, it is geographically uneven, biting hardest where fiscal credibility is weakest — the reverse of what a single policy rate aimed at the aggregate would deliver. Meanwhile the stance is not restrictive in real terms: the deposit rate is roughly zero against core inflation and about 1.3 points below headline.

Energy Inflation and Second-Round Effects

Official data. Headline HICP rose to 3.8% in the September flash from 3.2% in August and 2.9% in July, the highest since September 2023. Energy inflation reached 18.8% (14.3% in August), core edged up to 2.5% (2.4%) and services to 3.2% (3.0%, a four-month low in August). With energy at roughly a 9% weight, it contributes about 1.7pp of the 3.8% (LBMR calculation from Eurostat’s August contribution table), implying ex-energy inflation of around 2.3%. The shock is also uneven: September HICP was 3.4% in France (INSEE, provisional), 4.1% in Italy (ISTAT, provisional) and 5.0% in Spain (INE, flash), a dispersion of roughly 160bp under one policy rate.

First-round effects are large but self-limiting. They flow through fuel, refining margins on liquid fuels, gas and electricity, and they compress real incomes; staff project energy inflation to peak near 15% at the end of 2026 and turn negative in the second half of 2027. The second-round channels are where the judgement lies:

• Wages. Compensation per employee grew 3.3% in the second quarter, down from 3.6%; the ECB sees no material response to the energy shock so far (official).
• Pricing power. European Commission surveys show manufacturers’ selling-price expectations rising to 20.3 in September from 16.9, and consumers’ price expectations rose in August, although MUFG reads the surveys as pointing to limited non-energy price pressure.
• Expectations. Shorter-horizon measures are elevated, while most longer-term measures stand around 2% (ECB).

LBMR interpretation. Staff already embed partial pass-through, with core projected to rise to 2.6% in 2027 and second-round effects estimated at only 0.1–0.2pp in 2027–28, so the risk is not that second-round effects exist but that they exceed the baseline. Staff’s severe scenario, with stronger wage and non-energy price reactions, puts 2027 headline inflation at 5.4% and core at 3.5%. Services is the swing variable. The 0.2pp September rebound may reflect tourism- and transport-related base effects (INSEE, MUFG Research), but a second consecutive rise would change that reading. Unlike 2022, the shock arrives from inflation near target (2.2% in September 2025) with wage growth decelerating rather than accelerating. That supports a measured response; it does not guarantee one.

Financial and Global Transmission Channels

Sovereign yields and fiscal policy

Market data. The ECB sets the euro-area front end; the long end is set globally and fiscally. The 10-year Bund traded at about 3.4–3.6% on 1–2 October; the OAT at 4.94–4.95%, an 18-year high; and the OAT–Bund spread at about 133–142bp, the widest since 2012. France’s 2027 budget bill, presented on 1 October, aims to cut the deficit to 5% of GDP (Danske Bank). UBS strategists link the spread move to higher inflation risk, higher term premia and fiscal and political uncertainty reinforcing one another (Reuters), not to energy alone.

LBMR interpretation. Fiscal policy is pulling against the ECB. ECB staff put temporary energy-support measures (mostly lower indirect taxes and higher subsidies) at about 0.1% of GDP, estimate that defence and infrastructure spending, mainly in Germany, adds about 0.5pp to cumulative growth over 2025–28, and see the euro-area deficit peaking at 3.7% of GDP in 2027. Untargeted relief plus heavy issuance raises term premia just as monetary policy wants less demand, and the weakest issuer is repriced first. TPI is the answer to disorderly dynamics, but eligibility is conditional on sound fiscal and macroeconomic policies, which makes the French budget path a de facto input into monetary policy.

Banks, credit, housing and investment

Official data. Euro-area bank rates in August stood at 3.77% for new corporate loans and 3.60% for house purchase (ECB, published 1 October), data that pre-date the September repricing, so most of the pass-through from higher five- to ten-year yields is still ahead. Lagarde also noted that borrowing linked to artificial-intelligence investment accounts for roughly a quarter of credit growth to firms, and that US technology issuers are increasingly raising euro bonds, which may make financing costlier for other firms and sectors.

LBMR interpretation. From an ALM perspective, banks face offsetting effects: a higher front end supports net interest income, while higher long yields reduce the economic value of fixed-rate assets and mark down sovereign portfolios, re-opening the sovereign–bank link in the most exposed jurisdictions. Housing and investment respond more slowly but more durably than to the policy rate, through long-fixation mortgages and corporate bond pricing, and at a time when energy costs already compress margins. The hurdle rate for investment is rising before the hit to demand shows in the data.

The Fed, the BoJ and the global cost of capital

Official and market data. The Fed raised its range by 25bp to 3.75–4.00% on 16 September in a unanimous 12–0 vote, its first hike since July 2023; the BoJ raised its rate to 1.25% on 18 September by 7–2. Treasury yields on 2 October were 4.84% at two years, 5.28% at ten and 5.61% at thirty, with the 10-year having touched its highest level since 2002 in late September. The 10-year JGB reached about 3% in early September and the 30-year was auctioned at an average yield of 4.08% on 3 September and closed at 4.05% on 17 September. BMO measured a 0.96 one-month correlation between WTI crude and the 10-year Treasury yield in mid-September (CNBC), the tightest since 2019. Brent closed at $105–107 on 24 and 28 September and was around $101 on 5 October, against under $73 before the war. September US payrolls rose by only 29,000, which markets read as reducing the need for an October Fed hike.

LBMR interpretation. The energy shock is being transmitted through global term premia, not through the ECB, and the euro area is a price-taker on global duration: Bund yields sit roughly 175–185bp below Treasuries, yet every major long end now offers a competing yield. With oil and deficits as shared drivers, sovereign diversification offers less protection than in past cycles. The differentiation that remains is credibility, with the Bund trading as a safe haven within the euro area while the OAT does the opposite.

Scenario Analysis

We specify conditions and implied responses rather than assigning probabilities. The scenarios are LBMR constructs, not ECB guidance.

LBMR interpretation. Our central case is a hold on 29 October, consistent with Lagarde’s remarks, the pricing above and MUFG’s expectation that the next hike comes in December. Beyond that the data decide between A and B. Scenario C is where the reaction function is least predictable: the ECB would be choosing between its inflation mandate and sovereign stability, and the policy rate would not be the primary instrument.

Implications for Markets

• Euro rates. Front-end pricing is retreating from three to four further hikes, with MUFG treating two more hikes to 3.00% by early 2027 as largely priced, so it remains the most data-sensitive part of the curve: a services or wage surprise would reprice it quickly.
• Curve and spreads. The long end is driven by global term premia and French fiscal risk; intra-euro spreads are the barometer of transmission, and EUR/CHF has already begun to reflect it.
• Banks and credit. Income support from the front end competes with sovereign marks and a slower-moving credit-cost channel; higher funding costs for non-financial issuers have not yet shown in bank statistics.
• Equities. Higher discount rates weigh on long-duration earnings. Lagarde also warned that global equity valuations are concentrated in a few AI-related firms that are rapidly increasing their debt funding, a risk that could spill over to euro-area investors.
• FX and global. The euro weakened against the dollar in September, mainly on Fed repricing (MUFG), and EUR/USD slid below 1.13 on 1 October (Danske Bank). No G4 long end currently offers refuge; a durable Hormuz settlement is the main upside risk for bonds across regions.

Conclusion

The September repricing has changed the question. It is no longer only whether energy inflation will spread into wages, but whether the bond market’s tightening substitutes for the ECB’s or constrains it. The evidence supports partial substitution: long yields are slowing demand and giving the Council room to wait, but they are tightening through risk premia that are unevenly distributed, indifferent to wage-setting and vulnerable to the French fiscal path. The ECB can afford patience while services, wages and expectations behave. It cannot assume the long end will keep doing its work, nor that tightening delivered through spreads is the tightening it would have chosen.