According to @KobeissiLetter, the top 10 US stocks now account for 41.4% of the S&P 500’s market cap, an all-time high, indicating a highly concentrated index profile, source: @KobeissiLetter. @KobeissiLetter reports this share has risen by 6.2 percentage points since April 2025 and by 8.4 points since January 2024, highlighting rapid concentration gains over 18 months, source: @KobeissiLetter. @KobeissiLetter also notes the top 10’s combined market value has surpassed $25 trillion for the first time, now equal to 83% of the size of the US economy, underscoring Big Tech’s outsized weight in index performance and risk attribution, source: @KobeissiLetter. For traders, this data flags elevated concentration risk in S&P 500 exposure where a small cohort drives returns and drawdowns, making breadth-sensitive strategies and risk controls more critical, source: @KobeissiLetter.