The 'Magnificent 7' tech stocks add $150 billion of market cap in a day, with Microsoft leading the charge as investors zero in on the OpenAI psychodrama

• The "Magnificent Seven" mega-cap stocks' stellar 2023 continued Monday.
• The Big Tech giants added $150 billion to their combined market cap in a single day, driven higher by investors' renewed focus on AI.

The "Magnificent Seven" stocks' stellar 2023 continued Monday, as investors' renewed focus on artificial intelligence powered two of the group's members to fresh all-time highs.

Microsoft and Nvidia led the charge as the seven companies' combined market capitalization ballooned by $150 billion, according to data from Refinitiv.

The first of those two tech giants dominated headlines as CEO Satya Nadella announced the hiring of ousted OpenAI boss Sam Altman in one of the wildest coups in Silicon Valley history.

By the closing bell, shares had climbed 2% to hit a new record high. That boosted Microsoft's total valuation by $57 billion to $2.8 trillion overall, per Refinitiv.

Nvidia also enjoyed a strong start to the week as momentum built ahead of its third-quarter earnings, which are set to be released Tuesday.

Shares in the trillion-dollar chipmaker – whose dominant share of the graphics processing unit (GPU) market has made it the best-performing S&P 500-listed stock of 2023 – climbed another 2.3%, hitting a record high of their own.

Nvidia's market cap rose $27 billion to $1.2 trillion, Refinitiv data showed.

The other five Magnificent Seven stocks – Apple, Google owner Alphabet, Amazon, Facebook parent Meta Platforms, and Elon Musk's EV maker Tesla – also edged up on Monday, with their combined valuation swelling by $66 billion, by Business Insider's calculations.

The seven companies' increasing dominance of the S&P 500 has been one of the defining stories of 2023, with their strong performance this year driving most of the benchmark index's returns.

Their combined market cap now stands at $11.8 trillion, according to Refinitiv – almost three times the size of Germany's economy.