More than £400bn wiped off value of Google owner Alphabet as record-breaking Wall Street rout sparks fears of AI crash

Updated: 14:56 EDT, 29 October 2026 More than £400billion has been wiped off the value of Google owner Alphabet in one of the biggest stock market routs in history.In a turbulent session in New York, shares in the US technology giant plunged nearly 14 per cent in early trading on Thursday as investors fretted over its huge spending on AI infrastructure such as data centres.The fall slashed Alphabet’s value by around £406billion – the second biggest daily drop in market value in Wall Street history behind Nvidia’s £450billion slump in January last year.It marked the Google owner’s worst-ever session with the value lost equivalent to the entire market capitalisations of London-listed AstraZeneca, Rolls-Royce and Unilever combined.Alphabet was still valued at around £2.5trillion, however, some ten times more than Shell, the UK stock market’s biggest company. Shares in Google owner Alphabet tumbled in New York on ThursdayThe sell-off dragged down the tech-heavy Nasdaq, which fell nearly 2 per cent, and sparked fresh fears that the AI-driven stock market boom may turn to bust.The rout will be felt by millions of British savers – even if they do not own Alphabet shares outright – via exposure to the US stock market through funds in their ISAs and pensions.Neil Wilson, an investor strategist at Saxo, said: ‘A drop this size blows a big hole in all the major indices, it's not a pretty picture. It shows that investors don't just want capex, they want to see the returns already.’The sell-off came as Alphabet’s latest quarterly results sent shockwaves through the stock market.The company - one of the so-called Magnificent Seven US tech titans - said revenues jumped 25 per cent to £95billion in the three months to the end of September.But this missed Wall Street forecasts and profits fell by a quarter to £20billion as the company raised its spending on AI to close to £40billion.At the same time, the company revealed that its core advertising business is coming under pressure from the growing popularity of ‘AI Mode’, a new chatbot service on Google Search where the company is still experimenting with ads.Tracy Woo, principal analyst at Forrester, said: ‘The softer search performance is significant because it highlights the challenge of funding massive AI investments while maintaining the strength of established businesses.’Russ Mould, investment director at AJ Bell, said: ‘Vast spending on AI seems to be tolerated by investors if companies’ earnings are unblemished. This is where Google-owner Alphabet has fallen down.‘While overall revenue was solid in the quarter, the company saw weakness in its core search advertising business as it burns through cash at rates which would make the main character in Brewster’s Millions blush.‘There are clear signs that Google’s chatbot-style AI mode is hurting traditional search and while there was always likely to be a transition here, the deceleration in growth is still causing real disquiet.’He added: ‘Only time will tell if Alphabet’s expensive all-encompassing strategy of developing its own chips, data centres and large language models is the right one. The reaction to this latest update suggests that more than a few doubts persist in the market.’DIY INVESTING PLATFORMSAJ BellAJ BellEasy investing and ready-made portfoliosHargreaves LansdownHargreaves LansdownFree fund dealing and investment ideasinteractive investorinteractive investorFlat-fee investing from £4.99 per monthFreetradeFreetradeInvesting Isa now free on basic planTrading 212Trading 212Free share dealing and no account feeAffiliate links: If you take out a product This is Money may earn a commission. These deals are chosen by our editorial team, as we think they are worth highlighting. This does not affect our editorial independence.Compare the best investing account for you