xAI Colossus is the AI training supercomputer that xAI built inside a former Electrolux factory in southwest Memphis, Tennessee, and the system behind its Grok models. xAI says it built the first phase in 122 days and doubled it to 200,000 Nvidia H100 GPUs in 92 more days. As of October 2026 the company describes Colossus as one part of a larger complex straddling the Tennessee-Mississippi state line, and its own pages now carry the name SpaceXSI.
This explainer uses only the company’s own statements and filings and those of official local bodies: Memphis Light, Gas and Water (MLGW), the city utility, and the Greater Memphis Chamber.
On this page
What Colossus is
Colossus is a single GPU cluster built for training large models. On its Colossus page, xAI describes it as “200,000 H100 GPUs in a single interconnected cluster” and lists these system figures:
- 170 PB/s of aggregate memory bandwidth across the full system
- 2.8 Tb/s of network bandwidth per server for distributed training
- 0.5 EB of storage for training data and checkpoints
xAI calls the facility its “gigafactory of compute.” It says it was told the build would take 24 months and finished in four, and that the full timeline ran 276 days from groundbreaking, from May 2024 to February 2025.
The site is the former Electrolux manufacturing plant on Paul R. Lowry Road in the Frank C. Pidgeon Industrial Park, according to MLGW’s May 2025 public update. The industrial park also holds TVA’s Allen combined-cycle plant, the city’s Maxson wastewater treatment plant and Nucor Steel.
GPU counts, by date
xAI’s GPU figures have grown in steps, and each one is tied to a date by the company or the Chamber.
| Date | Milestone | Source |
|---|---|---|
| June 5, 2024 | Colossus announced for Memphis | Greater Memphis Chamber |
| August 8, 2024 | Colossus goes live, 122 days after the announcement | Greater Memphis Chamber |
| September 3, 2024 | 100,000 Nvidia H100 GPUs | Greater Memphis Chamber |
| December 4, 2024 | 200,000 H100 GPUs | Greater Memphis Chamber; xAI |
| May 1, 2025 | Phase I at full operational capability on 150 MW of grid power | Greater Memphis Chamber |
| End of 2025 | Colossus I and II: “over one million H100 GPU equivalents” | xAI, January 6, 2026 |
| July 30, 2026 | Fixed timeline to remove 69 temporary turbines at Southaven | SpaceXSI |
| September 30, 2026 | 1.7 GW of nameplate compute in SpaceX’s SI segment, as the COLOSSUS II buildout continued | SpaceX, October 20, 2026 |
The end-2025 figure is stated in “H100 GPU equivalents,” not in physical H100 chips, and it covers Colossus I and Colossus II together. xAI gave it in its Series E announcement on January 6, 2026. The company’s Memphis page says it plans to equip the facility with 1 million GPUs, and the Chamber’s FAQ puts that target in 2026.
Latest capacity figure
Since xAI became part of SpaceX, the operator reports compute capacity in gigawatts rather than GPU counts. In its third-quarter 2026 results, filed with the SEC on October 20, 2026, SpaceX said its Super Intelligence (SI) segment expanded nameplate compute to 1.7 GW as of September 30, 2026, up from 1.4 GW on June 30, 2026 and 0.6 GW a year earlier, “as we continued the buildout of COLOSSUS II.” The 1.7 GW is the segment’s total nameplate compute, not a figure for the original Colossus building alone, and it describes installed capacity rather than measured power draw.
How Colossus is powered
Power is the most documented part of the project, and MLGW’s public updates set out the grid side.
xAI asked MLGW and TVA for two successive 150 MW increments at the Paul R. Lowry Road site, 300 MW in total. For the first increment, the utilities completed impact studies, xAI paid for transmission upgrades and a new substation, and the TVA board approved the supply. In May 2025 MLGW said the site was drawing 150 MW: 8 MW from an existing substation and 142 MW from the new one. A second substation for the next 150 MW was under construction at xAI’s expense, and MLGW projected the additional power by no later than December 2025, subject to TVA approval.
MLGW also states that xAI pays the prevailing industrial rate and has signed an agreement with TVA and MLGW to curtail its grid consumption when demand is high.
The Greater Memphis Chamber’s May 2025 release adds that the 150 MW of grid power arrives through substation #63 and that 150 MW of Tesla Megapack batteries were integrated as backup, to ride through outages and demand-response events. The Chamber’s FAQ says xAI spent $35 million building that substation and committed $20 million to another.
The Chamber describes the natural gas turbines used in the early phase as temporary, a way to power the supercomputer without drawing on the Memphis grid, and says they would eventually serve only as backup.
Colossus 2 and the Southaven power plant
xAI’s footprint now extends beyond the original building. The Chamber lists several xAI sites in the Memphis area: Colossus, Colossus 2 and the Colossus Water Recycling Facility. MLGW identifies the second large facility as being on Tulane Road, close to the state line and near TVA’s Southaven combined-cycle plant. In its May 2025 update, MLGW said it had received an initial request for 260 MW of grid power at Tulane Road, and that options from 260 MW to 1.1 GW had been discussed, with a final request still to come.
On July 30, 2026, the company, now signing as SpaceXSI, published a site update describing its goal as “the world’s largest integrated supercomputer at the Tennessee-Mississippi state line.” The update says:
- The company entered an agreed order with the Mississippi Department of Environmental Quality setting a fixed removal timeline for all 69 temporary mobile turbines that power its facility in Southaven, Mississippi.
- Removal can begin as early as August 2026, and all temporary turbines are to be gone by July 2027.
- They are being replaced by a 1.2 GW permanent power plant of 41 turbines, authorized under a Clean Air Act permit granted in March 2026.
- All of its mobile turbines are being fitted with selective catalytic reduction to cut nitrogen oxide emissions.
Water and land
According to the Chamber, xAI trucked in water to cool Colossus and recycled it through a closed-loop system rather than drawing from the aquifer. xAI has committed to an $80 million wastewater recycling facility. The Chamber says the plant can keep up to 4.7 billion gallons of water a year in the Memphis aquifer, about 9% of the load, and can also supply other industrial users.
The Chamber also says xAI is leasing 552 acres in the Frank C. Pidgeon Industrial Park for expansion and bought a separate site for the recycling plant.
Key figures
| Item | Figure | Source |
|---|---|---|
| GPUs in the original cluster | 200,000 Nvidia H100 | xAI |
| Aggregate memory bandwidth | 170 PB/s | xAI |
| Network bandwidth per server | 2.8 Tb/s | xAI |
| Storage | 0.5 EB | xAI |
| SI segment nameplate compute, September 30, 2026 | 1.7 GW | SpaceX |
| Grid power at Paul R. Lowry Road | 150 MW, with a second 150 MW requested | MLGW |
| Battery backup | 150 MW of Tesla Megapacks | Greater Memphis Chamber |
| Southaven permanent power plant | 1.2 GW, 41 turbines | SpaceXSI |
| Wastewater recycling plant | $80 million | Greater Memphis Chamber |
Live records for Colossus and other projects are in our AI data centers tracker, and the accelerators inside them are compared in AI chips.
