TL;DR

Borrowing costs adjusted for inflation have climbed to their highest level in over ten years across the major economies, and the flood of bonds funding AI infrastructure is a leading reason. British and German ten-year real yields are both at decade highs. Analysts warn the same mechanism that has been lifting equities could end up choking them.

The scale of the issuance

Alphabet, Amazon and Meta between them have sold close to $220bn of bonds during 2026, against $108bn across the whole of 2025, on LSEG figures. That doubling arrives while governments are still borrowing heavily — a US deficit near 6% of output, France at 5%, Britain at 4%.

Buyers respond to that supply by demanding more. US thirty-year real yields sit near eighteen-year highs at about 3%, and the Treasury paid 5.22% at auction on Thursday, the steepest since 2001. BlackRock Investment Institute’s UK chief investment strategist, Vivek Paul, described a contest for capital with few recent parallels, accelerated by the AI build-out.

What it means for British readers

This is the transmission line from AI capital spending to household finances, and it runs through the gilt market. Real yields set the inflation-adjusted cost of borrowing for the government and for companies; when they rise across the curve, the pricing of fixed-rate mortgages and corporate credit follows, regardless of what the Bank of England does with its policy rate.

Mirabaud’s Al Cattermole makes the case that European yields are being driven more by defence, energy security and infrastructure than by AI specifically. That is a fair qualification, though it does not much help a UK borrower: the causes differ, the cost does not.

The warning

Matt King of Satori Insights expects real yields to keep climbing until they shut off the borrowing driving them — and, with it, the rotation into risk that has fuelled the equity rally. Ashok Bhatia at Neuberger reckons US real yields remain under the 3-4% band where growth starts to suffer, while calling current levels a warning sign.

Equities have so far ignored all of it, with JPMorgan lifting its S&P 500 earnings forecasts and European blue-chip profits growing at their quickest pace since late 2022.

Looking forward

The awkward possibility is that the AI trade breaks on its financing rather than its technology. UK firms modelling capital expenditure for 2027 should test it against materially higher real borrowing costs, not against the rates that made the past two years’ plans look affordable.