Microsoft shares slide as Anthropic filing shows $1B stake

Microsoft ↘ 2.46% shares fell for a second day on Wednesday, November 11, after Anthropic's amended IPO filing listed the software giant as one of seven strategic buyers in a $26 billion private placement. Microsoft's share comes to about $1 billion, or 13,513,513 shares at the $74 midpoint of the price range, according to GuruFocus via TradingView. The filing shows how closely Microsoft is now tied to a company that has also started competing directly with Office.tradingview.com

What the filing shows

Anthropic filed Amendment No. 2 to its Form S-1 on November 10, offering 825 million shares at $70 to $78 each, Fortune reported. According to the registration statement, Google, Nvidia ↗ 3.53%, Advanced Micro Devices ↗ 7.99%, Broadcom ↗ 4.57%, Micron Technology ↗ 12.29%, Microsoft and TSMC Partners will buy nonvoting Class N stock at the IPO price right after the offering closes. The deal depends on the IPO going through. Google and Nvidia are each putting in $10 billion and AMD $2.5 billion. Broadcom, Micron and Microsoft are each committing $1 billion, while TSMC Partners is investing $500 million, The Economic Times reported. The amendment also says Anthropic's annualized revenue run rate reached about $81 billion at the end of October, according to Fortune. The offering could value the company at up to $1.4 trillion.fortune.com+3

Partner and rival

The stake is small compared with Microsoft's market value of about $3.97 trillion. GuruFocus said its value lies in Microsoft's position: the company gains exposure to a model maker that already sells Claude through Azure, while Claude could increasingly compete with Microsoft's own software.tradingview.com

That competition is already moving the stock. On Tuesday, Microsoft shares dropped as much as 3% midday after Anthropic released new Claude workplace tools that could rival Office, CNBC reported. The tools include Claude Sheets, a spreadsheet app, and they come at no extra charge with paid Claude plans, Yahoo Finance noted. Investing.com said the competitive pressure, insider selling by the CFO and concerns about inflation data kept Microsoft lower on Wednesday, even as other tech stocks recovered.finance.yahoo.com+2

Deep financial ties

The two companies' relationship goes back further. In November 2025, Microsoft agreed to invest up to $5 billion in Anthropic, and Anthropic committed to buying $30 billion of Azure computing capacity. Microsoft booked a $3.2 billion gain on that stake in its June quarter. Investing.com said the IPO is scheduled to price on November 18. It described an "unusual dynamic where backing a rival's growth story may come at the cost of its own valuation."ibtimes.com+2