AI sentiment swings from fear to greed, whipsawing tech stocks

September 27, 2026 at 06:00 PM2 min

This digest was compiled by AI from multiple sources — links to the originals are below.

AI-related stocks swung sharply over the past two weeks as investor sentiment lurched from existential fear to exuberance. The Nasdaq 100 erased more than $600 billion in market value after Anthropic CEO Dario Amodei called for a slowdown in AI development on Sept. 12, then rebounded to a record as Meta's Muse assistant fueled renewed optimism. The volatility also hit subscription-based companies as AI agents threaten pricing power.

Key Facts

Anthropic CEO Dario Amodei called for a slowdown in AI development on Sept. 12, backed by OpenAI CEO Sam Altman and SpaceX CEO Elon Musk.
The Nasdaq 100 dropped 1.5% between Sept. 14 and 15, erasing more than $600 billion in market value.
Meta shares jumped 11% on Monday, putting the company on pace for its best month in more than a decade.
The Philadelphia Semiconductor Index gained 6% on Monday and Tuesday, helping push the Nasdaq 100 to its first record since early June.
Allstate fell 8.9%, Charter Communications sank 12%, and Planet Fitness shed 14% this week as AI agents threaten subscription pricing.

AI Slowdown Fears

Anthropic CEO Dario Amodei called for a slowdown in development of cutting-edge AI models on Sept. 12. OpenAI CEO Sam Altman and SpaceX CEO Elon Musk quickly backed the call. The warnings validated recent industry concerns about existential risks from AI. On the first trading day after Amodei's essay, AI infrastructure stocks tumbled on fears of reduced computing equipment spending. CoreWeave and Lam Research fell more than 9% during the selloff.

Market Rebound

Excitement about Meta Platforms' Muse personal assistant sent traders rushing back into AI-exposed stocks last week. Meta shares jumped 11% on Monday, putting the company on pace for its best month in more than a decade. Arm Holdings jumped 17% on Monday, while Intel and Advanced Micro Devices each rallied more than 9%. The Philadelphia Semiconductor Index gained 6% on Monday and Tuesday. The Nasdaq 100 reached its first record since early June.

Subscription Model Pressure

The AI rally triggered selloffs in companies relying on recurring bills and negotiable pricing. AI agents are expected to improve at price comparison, trip bookings, and customer service interactions. Allstate fell 8.9% this week, while Charter Communications sank 12%. Planet Fitness shed 14% amid the shift.