TL;DR
SemiAnalysis forecasts about 51.2 GW of new data center capacity outside mainland China in 2027, while Altimeter Capital founder Brad Gerstner publicly argued actual delivery would be close to 25 GW. The roughly two-fold gap stems mainly from different judgments on construction progress, lease constraints and delivery pace.
Comparison Overview
In September 2026, Altimeter Capital founder Brad Gerstner challenged SemiAnalysis's earlier 43 GW forecast at the All-In Summit, arguing 2027 delivery would be close to 25 GW. On October 25, 2026, SemiAnalysis released "Datacenters 2027: The Year of Acceleration," updating its 2027 forecast to 51.2 GW and directly addressing the criticism.
Comparison Table
| Dimension | SemiAnalysis | Altimeter Capital (Brad Gerstner) |
|---|---|---|
| 2027 new capacity forecast | About 51.2 GW | Close to 25 GW |
| Primary basis | Satellite imagery (24.3 GW late-stage), leases (~$1 trillion), self-build starts | Skepticism about delivery pace, funding and power constraints |
| Scope | Global market excl. mainland China | Global market (scope differs) |
| Release time | October 25, 2026 | September 2026 (All-In Summit) |
| Stance | The buildout boom continues and accelerates | The market is overly optimistic about delivery scale |
Evidence and Positions
SemiAnalysis's three evidence classes: about 40 campuses totaling over 24.3 GW in late-stage construction, most more than half complete; leases signed in 2026 YTD slightly below $1 trillion with Meta, AWS, Microsoft, Google, NVIDIA, AMD, Anthropic and OpenAI seeking gigawatt-scale deals; and parabolic growth in quarterly megawatt starts by U.S. hyperscalers.
Altimeter's skeptical stance: Gerstner argues the AI infrastructure boom contains over-promising, and actual delivery will be constrained by grid access, supply chains and funding, coming in well below optimistic forecasts.
Interpreting the Disagreement
The divergence first stems from scope: SemiAnalysis explicitly states "excl. mainland China," while Gerstner's 25 GW figure is not region-limited, so direct comparison is imperfect. Second, the two sides judge the conversion from signed leases to actual delivery differently: SemiAnalysis uses satellite imagery to show construction is real, while Altimeter argues leases-to-installation retains substantial uncertainty. SemiAnalysis responded in the report: "We focus on facts, not narratives." The report also concedes that even if data halls are delivered on schedule, chip and HBM supply will determine actual compute deployment speed in 2027-2028 — partially converging with the constraints the skeptics emphasize.
Data Sources
- SemiAnalysis "Datacenters 2027: The Year of Acceleration" (published October 2026)
- Xinzhi Times via Sina Finance: 51.2 GW forecast for 2027 global AI capacity (October 25, 2026) link