U.S. stocks opened the fourth quarter higher as AI-related shares and chipmakers advanced, but Alphabet fell 2% to $338.85 after Google unveiled Gemini 4 Argon. An earlier account reported Alphabet up about 2%, or 1.7%, making the later account more specific on the immediate market reaction. Google said Argon targets long-horizon enterprise work, complex software development, automated cybersecurity and potentially more complex tasks within Spark, its personal-agent product. The model can process up to 1 million tokens in a single trajectory, scan codebases, identify critical vulnerabilities and write context-aware security patches. Google said early testing found a severe, previously unmapped vulnerability in hospital healthcare software that earlier models missed, while its internal engineering infrastructure is already using Argon. Argon is initially available only to trusted cybersecurity specialists through Google’s Fairwind Program. Enterprise users, developers and subscribers are expected to receive access after additional safety safeguards are added, with an introductory developer price of $2 per million input tokens. Google’s Gemini product chief told CNBC the company is exploring whether Argon could power more complex Spark tasks, while Spark remains behind a paywall and Meta’s free Muse gains traction. The limited rollout leaves demand and near-term revenue untested.