US markets close 21 September 2026: Nasdaq +2.26% to a record as Meta's MUSE agent reprices server CPUs

S&P 500 close: 7,764.70 (+1.49%) Sentiment: bullish

The S&P 500 closed at 7,764.70 on 21 September 2026, up 114.20 points or 1.49%, after Meta launched its MUSE AI agent and buyers moved into data-centre CPU suppliers. META.US rose 11.43% to $741.25 and ARM.US gained 17.16% to $322.90, with Arm CEO Rene Haas citing US$2 billion of booked customer demand for the new AGI CPU. Crude oil fell 4.28% to US$91.97 as Saudi Arabia moved to restore roughly half its East-West pipeline capacity, and the US 10-year yield eased 3.5 basis points to 4.963%.

What moved the index

• Information technology (XLK.US +2.89%): about 37% of the index at roughly 108 bps of the 149 bps move. INTC.US +12.14%, AMD.US +9.95%, QCOM.US +9.29% and ALAB.US +12.36% on the MUSE server-CPU demand bet. The Philadelphia semiconductor index closed +4.29%.
• Communication services (XLC.US +3.90%): about 10% of the index at roughly 38 bps. META.US +11.43% on the MUSE launch, plus WBD.US +10.79% as Paramount Skydance advanced antitrust settlement talks with California's attorney general over its $31.00 per share cash bid.
• Energy (XLE.US -2.30%): about 3% of the index at roughly -8 bps. The 4.28% crude fall hit refiners hardest: PBF.US -6.10%, DINO.US -5.70%, MPC.US -5.30%, VLO.US -4.84%.
• The other eight sectors: XLY.US +1.30%, XLRE.US +0.98%, XLV.US +0.75%, XLF.US +0.42%, XLI.US +0.40%, XLB.US -0.10%, XLU.US -0.34%, XLP.US -0.41%, worth about +14 bps net.

Technology and communication services alone account for roughly 146 of the 149 bps. Sector ETF returns are capped-weight proxies rather than exact GICS index returns, so this attribution runs a little hot.

Session highlights

• INTC.US +12.14% to $121.78 was the strongest S&P 500 component. AMD.US +9.95% to $615.52 closed near a US$1 trillion market value. QCOM.US +9.29% to $194.23.
• 2,875.36 on the Russell 2000, up 0.52%, against the Nasdaq Composite at +2.26%. Leadership stayed narrow and large-cap.
• VIX finished at 14.87, up 0.06 points, inside a 14.60 to 15.13 range.
• BTC-USD +7.21% carried MSTR.US +9.47% to $168.50.
• Gold fell 0.99% to US$4,381 an ounce while the dollar index rose 0.18% to 100.404.

Sector scorecard

• Best: communication services, XLC.US +3.90%
• Worst: energy, XLE.US -2.30%
• Dispersion (best minus worst): 6.20 points
• Four of eleven sectors closed lower: energy XLE.US -2.30%, consumer staples XLP.US -0.41%, utilities XLU.US -0.34% and materials XLB.US -0.10%.

Top movers

After-hours earnings

The after-the-bell calendar was thin on 21 September. ABVX.US was the only scheduled reporter of any size, and it closed the regular session at $103.45, down 1.51%. No S&P 500 constituent released results after the 16:00 ET bell.

Notable announcements

• MRNA.US +12.27% to $172.94 after its Phase 3 melanoma mRNA vaccine data won a presidential symposium slot.
• AKAM.US +12.33% to $117.41 on its pitch to sell identity and access control for AI agents.
• DOCN.US +12.31% to $146.16, after last week's $725m AI infrastructure commitment.
• NVO.US -7.96% to $39.80 after a London Capital Markets Day left the 2032 US semaglutide patent expiry unaddressed.
• GRML.US +230.53% to $9.42 on a weekend US security agreement with Denmark covering Greenland.

Next session catalysts (ET)

• Tue 22 Sep: Chicago Fed National Activity Index
• Wed 23 Sep: S&P Global flash manufacturing and services PMIs, Richmond Fed manufacturing index, Q2 current account, API crude inventories
• Wed 23 Sep: FDA Molecular and Clinical Genetics Panel votes on the Galleri premarket approval application (GRAL.US)
• Wed 23 Sep: Xi Jinping arrives at Joint Base Andrews
• Thu 24 Sep: White House state dinner for Xi Jinping, with Musk, Bezos, Huang, Altman, Pichai, Dell, Fraser and Cook confirmed on the guest list
• Later this week: weekly initial jobless claims, durable goods orders and the final Q2 GDP print

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