xAI Colossus

Colossus is an artificial-intelligence supercomputer and GPU training cluster in Memphis, Tennessee, built by xAI and owned since February 2026 by SpaceX, which acquired xAI. It is widely described as one of the largest single-site AI GPU clusters in the world. Its first phase, comprising roughly 100,000 NVIDIA H100 accelerators, was built in 122 days and came online over the Labor Day weekend of 2024; xAI then doubled it to about 200,000 GPUs in 92 days by adding H200 parts, and by July 2025 it held about 230,000 GPUs, including 30,000 GB200s. ^[1][2][3] Colossus was built to train xAI's Grok family of large language models. A far larger second site, Colossus 2, took over Grok training by 2026, and in May 2026 Anthropic agreed to use all of the original cluster's capacity. ^[4]

Colossus has also become the focus of an environmental and public-health dispute in Memphis over the methane gas turbines used to power the facility, which the NAACP, represented by the Southern Environmental Law Center (SELC), said were installed and operated without the air-quality permits required under the Clean Air Act. ^[5][6] Ownership changed twice in under a year: xAI merged with the X social network in March 2025, and SpaceX announced on February 2, 2026 that it had acquired xAI, folding the AI lab and Colossus into Elon Musk's spaceflight company; the AI business was renamed SpaceXAI in July 2026. ^{[7][8][9][10]}

What is Colossus?

Colossus is an AI supercomputer that xAI marketed as the world's largest, built around NVIDIA Hopper-generation GPUs networked with high-bandwidth Ethernet in a repurposed factory in South Memphis. ^[11][13] At NVIDIA's October 2024 announcement, an xAI spokesperson said "xAI has built the world's largest, most-powerful supercomputer" and that "NVIDIA's Hopper GPUs and Spectrum-X allow us to push the boundaries of training AI models at a massive-scale," and Elon Musk called Colossus "the most powerful training system in the world." ^[11] The "world's largest" claim could not be independently verified, because rival operators do not publish comparable figures and because total GPU counts shifted rapidly with each expansion. Since 2025 the first site has been referred to as Colossus 1, to distinguish it from the much larger Colossus 2 nearby. ^[3][12]

The system's defining characteristics are its scale and the speed at which it was assembled. xAI and NVIDIA said the facility and supercomputer were built in 122 days, and NVIDIA said only 19 days elapsed between the first rack rolling onto the floor and the start of model training. ^[11][2] xAI then doubled the cluster's size in 92 days. ^[2]

How was Colossus built so fast?

xAI sited Colossus in a former Electrolux appliance plant in South Memphis: a 785,000-square-foot main building on 217 acres, with a cooling tower and heavy electrical power feeds, which xAI leased from Phoenix Investors. ^[13] Electrolux had announced in January 2019 that it would close the plant, with production expected to continue through 2020. ^[14] Reusing an existing industrial shell allowed the company to skip much of the timeline normally associated with greenfield data center construction; xAI says it was told the build would take 24 months, and NVIDIA said systems of this size typically take "many months to years." ^[2][11]

Build partners Dell Technologies and Supermicro supplied and integrated the server hardware, while NVIDIA provided the GPUs and networking platform. ^[1][15][11] The first phase reached an operational 100,000-GPU configuration over the Labor Day weekend of 2024, and NVIDIA announced the networking details that October. ^[1][13][11] On December 4, 2024, xAI announced that it would expand Colossus to a minimum of one million GPUs, with NVIDIA, Dell and Supermicro also setting up operations in Memphis. ^[16] Through 2025 xAI added newer accelerators to the first site and began the separate Colossus 2 buildout. ^[3][12]

How many GPUs does Colossus have?

The cluster is built from Supermicro 4U liquid-cooled servers, each containing one NVIDIA HGX H100 board with eight GPUs and two x86 CPUs. Eight such servers fill a rack, giving 64 GPUs per rack, with a coolant distribution unit at the bottom of each rack; racks are grouped in eights of 512 GPUs, and the initial cluster comprised four data halls of 25,000 GPUs each. ^[15] Networking uses the NVIDIA Spectrum-X Ethernet platform rather than InfiniBand, with Spectrum SN5600 switches and a BlueField-3 SuperNIC for each GPU, each on a 400 Gb/s link. ^[11][15] NVIDIA reported that the fabric maintained 95 percent data throughput, enabled by Spectrum-X congestion control, with zero application latency degradation or packet loss from flow collisions, compared with about 60 percent throughput for standard Ethernet at this scale. ^[11]

Reported GPU counts by phase are summarized below. Figures come from xAI, Musk and press reporting; later totals mix multiple GPU generations.

How is Colossus powered and cooled?

Power has been the most constrained resource at the site. Memphis Light, Gas and Water (MLGW) initially supplied 50 megawatts, the Tennessee Valley Authority board approved 150 megawatts for the facility on November 7, 2024, and by May 2025 MLGW had completed a substation capable of supplying 150 MW. ^[17][18] SemiAnalysis estimated Colossus 1's power at about 300 MW in 2025, and the May 2026 Anthropic agreement covered more than 300 MW of capacity. ^[12][4] To bridge the gap between demand and available grid capacity, xAI installed natural-gas turbines on the property starting in June 2024. Aerial images in spring 2025 showed 35 turbines with a combined capacity of about 422 megawatts, and thermal imagery appeared to show heat plumes from 33 of them. ^[6][19][18] The company also installed 168 Tesla Megapack battery units, which the build team found helped buffer the millisecond-scale spikes and drops in power draw that GPU training produces; xAI said they also protect against outages. ^[19][15]

The servers are liquid-cooled: each rack's coolant distribution unit passes heat to facility water, which is cooled by chillers outside the building and recirculated. ^[15] MLGW said in 2024 that the site would need about a million gallons of water per day at full capacity. ^[13] xAI announced in February 2025 an $80 million plant, on land acquired from the city of Memphis, to recycle up to 13 million gallons of wastewater a day. Construction began in September 2025 but stalled in April 2026, and in June 2026 SpaceXAI committed to the city to resume it no later than the first quarter of 2027. ^[20]

What is Colossus 2?

xAI has been developing a second and substantially larger site, generally called Colossus 2, in the Memphis metropolitan area. It bought a warehouse and adjacent land in Memphis for the data center in March 2025 and generates power at a former Duke Energy power plant site across the state line in Southaven, Mississippi. ^[12] Musk said in July 2025 that the first batch of 550,000 GB200 and GB300 GPUs would start coming online at Colossus 2 within weeks, with a long-term ambition of roughly one million GPUs across the combined sites dating from the December 2024 expansion plan. ^[3][16] SemiAnalysis described Colossus 2 in September 2025 as the world's first gigawatt datacenter, and it came online in January 2026. ^[12][4]

The expansion accelerated at the end of 2025. On December 30, 2025, Musk said on X that xAI had bought a third building, which he named "MACROHARDRR" in a continuation of his "Macrohard" project, whose name plays on Microsoft's, and that it would take xAI's training compute to almost 2 gigawatts; the building is in Southaven. ^[21][22] In August 2026, Tom's Hardware reported that SpaceX's xAI data centers in Memphis and Southaven had a rated power draw of 1.4 GW and that Musk had told SpaceX employees he aimed for 10 GW by the end of 2027. ^[23] On September 25, 2026, Musk posted that Colossus 2 held 110,000 GB200 and 440,000 GB300 GPUs and that up to 660,000 more GB300s would come online in three waves of 220,000 by late December 2026, the last "if we get lucky." ^[24]

What is Colossus used for?

Colossus exists primarily to train xAI's models. The cluster was built to train the company's Grok chatbot, and Musk said in July 2025 that its GPUs were used for training while inference was handled by xAI's cloud providers. ^[3] The cluster's role changed in May 2026. On May 6, 2026, Anthropic agreed to use all of the compute capacity at Colossus 1, more than 300 megawatts across more than 220,000 NVIDIA GPUs, to add capacity for Claude subscribers; Musk wrote that he was "ok leasing Colossus 1 to Anthropic, as SpaceXAI had already moved training to Colossus 2." ^[4] xAI had announced in April 2026 that the AI coding company Cursor would also use Colossus capacity. ^[4]

SpaceX's S-1 filing showed Anthropic paying $1.25 billion per month through May 2029, at a discounted rate for the first two months, with either party able to terminate on 90 days' notice; TechCrunch calculated that the deal could bring in more than $40 billion. ^[25] On May 28, 2026, Musk said that "SpaceX has not committed to leasing Colossus for years, although it's possible that may be what happens," describing a 180-day lease followed by mutual 90-day cancellation rights. ^[26]

Who owns Colossus?

xAI, the AI company Elon Musk founded, built Colossus in 2024. On March 28, 2025, xAI acquired the X social network in an all-stock deal that valued xAI at $80 billion and X at $33 billion. ^[7] On February 2, 2026, SpaceX announced that it had acquired xAI, making the AI lab and Colossus part of the same company as SpaceX's launch business and the Starlink satellite-internet network. ^[8] CNBC reported that the transaction valued SpaceX at $1 trillion and xAI at $250 billion, a combined $1.25 trillion that made it the largest merger of all time, and Reuters reported that xAI investors would receive 0.1433 SpaceX shares for each xAI share. ^[9][27] Musk framed the deal in part as a step toward orbital data centers. ^[8]

SpaceX then went public: it priced its initial public offering at $135 per share on June 11, 2026, raising about $75 billion, with trading under the ticker SPCX. ^[28] In July 2026 the AI business, a SpaceX subsidiary, was renamed SpaceXAI, and press coverage from mid-2026 on refers to the Colossus operator under that name. ^[10][20] The mechanics, valuations, and downstream effects on Colossus are covered in detail in the SpaceX-xAI merger article.

Why is Colossus controversial?

Colossus has been at the center of a sustained dispute over air quality in South Memphis. The facility sits about a mile from Boxtown, a historically Black neighborhood founded after the Civil War, in an area that environmental advocates describe as already carrying a heavy industrial-pollution burden. ^[13] NPR, citing a ProPublica analysis, reported that the cancer rate in South Memphis is four times the national average, a figure the NAACP repeated for Boxtown in June 2025 and state Representative Justin J. Pearson cited in July 2025. ^[13][5][29]

The dispute centers on the gas turbines. In a June 2025 notice of intent to sue, the SELC, acting on behalf of the NAACP, said xAI had installed and operated the turbines "without any permits or best available pollution controls," citing aerial images that showed 35 turbines at the site. ^[5] The Shelby County Health Department approved a permit on July 2, 2025 for 15 permanent turbines; xAI removed its unpermitted turbines after the SELC's notice and said it would keep the 15 permitted units as backup power with selective catalytic reduction controls. ^[30][6][18] In July 2025, before the removals were complete, the Tennessee Lookout reported 33 turbines running at the site. ^[29] An appeal of the permit was dismissed as moot by the Memphis and Shelby County Air Pollution Control Board in December 2025. ^[31]

The conflict escalated to litigation over the second campus. In Southaven, xAI's subsidiary MZX Tech began running trailer-mounted turbines in August 2025 under a Mississippi Department of Environmental Quality (MDEQ) exemption for "temporary-mobile" units that run for less than 12 months. ^[32] On April 14, 2026, the NAACP and its Mississippi State Conference, represented by Earthjustice and the SELC, sued xAI and MZX Tech under the Clean Air Act in the U.S. District Court for the Northern District of Mississippi, alleging that 27 turbines were operated at the Colossus 2 power plant in Southaven between August and December 2025 without an air permit. ^[22][33] The complaint asserts that the plant has the potential to emit more than 1,700 tons of smog-forming nitrogen oxides per year. ^[33][6] After xAI added six more turbines, the plaintiffs put the potential for 33 turbines at 2,508 tons and asked for a preliminary injunction on May 6, 2026. ^[35] xAI argued that no federal permit was required because the turbines were temporary. ^[22] In June 2026 the U.S. Justice Department intervened on xAI's side and, along with Mississippi Governor Tate Reeves and a Defense Department official, asked the court to dismiss the case, while xAI argued that the NAACP lacked standing; Southaven residents filed a separate federal class action over turbine noise the same month. ^[36][37]

Mississippi's Environmental Quality Permit Board unanimously approved a construction permit on March 10, 2026 for MZX Tech to install 41 permanent gas turbines to replace the temporary units. ^[34] The temporary fleet kept growing, from 18 units in August 2025 to 27 in December 2025, 46 or 47 in May 2026 depending on the report, and 69 by July 2026, none of them with an air permit. ^[38][37][32] On July 30, 2026, MDEQ set a retirement schedule under which xAI agreed to begin removing the temporary turbines on August 18, 2026, while allowing 13 of them to run past the 12-month limit; xAI said it was building a permitted 1.2-gigawatt power plant. ^[32] Memphis residents filed another federal class action over turbine noise and vibration on September 23, 2026. ^[40]

The regulatory backdrop shifted in January 2026, when the U.S. Environmental Protection Agency published updated performance standards for stationary combustion turbines that add a subcategory for turbines used in temporary applications. ^[39] SELC attorney Amanda Garcia argued that the EPA still requires such turbines to have permits, while MDEQ said the rule "does not mandate that permitting authorities issue air permits for temporary turbines." ^[38]

Why does Colossus matter?

Colossus showed how quickly hyperscale AI training infrastructure can be deployed: xAI compressed a build it says it was told would take 24 months into 122 days by reusing an existing building, standardizing on liquid-cooled NVIDIA GPU racks, and adopting Ethernet rather than InfiniBand at this scale. ^[2][11] At the same time, it has become a prominent example of the tension between rapid AI expansion and local environmental and public-health concerns, particularly where on-site fossil-fuel generation is used to meet power demand that the grid cannot immediately supply. ^[6][22] The combination of record build speed, contested scale claims, and active Clean Air Act litigation over its power supply has made the Memphis complex a recurring reference point in debates over the costs and siting of AI compute. ^[12][33]

References

1. ^1 ^2 ^3 ^4 ^5xAI Colossus: The Elon Project - HPCwire, September 5, 2024.
2. ^1 ^2 ^3 ^4 ^5 ^6 ^7Colossus - xAI (page as archived July 2025 and June 2026).
3. ^1 ^2 ^3 ^4 ^5 ^6Elon Musk: 230K AI GPUs train Grok at Colossus 1: 550K GB200, GB300s at Colossus 2 coming soon - TweakTown, July 24, 2025.
4. ^1 ^2 ^3 ^4 ^5 ^6Anthropic to use all of SpaceX-xAI's Colossus 1 data center compute - DataCenterDynamics, May 6, 2026.
5. ^1 ^2 ^3Elon Musk's xAI threatened with lawsuit over air pollution from Memphis data center, filed on behalf of NAACP - NAACP, June 17, 2025.
6. ^1 ^2 ^3 ^4 ^5xAI built an illegal power plant to power its data center - Southern Environmental Law Center, updated April 14, 2026.
7. ^1 ^2 ^3Elon Musk says xAI has acquired X in deal that values social media site at $33 billion - CNBC, March 28, 2025.
8. ^1 ^2 ^3 ^4Elon Musk's SpaceX officially acquires Elon Musk's xAI, with plan to build data centers in space - TechCrunch, February 2, 2026.
9. ^1 ^2 ^3Musk's xAI, SpaceX combo is the biggest merger of all time, valued at $1.25 trillion - CNBC, February 3, 2026.
10. ^1 ^2 ^3Elon Musk's xAI has a new name. You can probably guess it. - Mashable (via Yahoo Finance), July 7, 2026.
11. ^1 ^2 ^3 ^4 ^5 ^6 ^7 ^8 ^9 ^10 ^11NVIDIA Ethernet Networking Accelerates World's Largest AI Supercomputer, Built by xAI - NVIDIA Newsroom, October 28, 2024.
12. ^1 ^2 ^3 ^4 ^5 ^6xAI's Colossus 2: First Gigawatt Datacenter In The World - SemiAnalysis, September 16, 2025.
13. ^1 ^2 ^3 ^4 ^5 ^6 ^7How Memphis became a battleground over Elon Musk's xAI supercomputer - NPR, September 11, 2024.
14. ^Electrolux closing Memphis facility amid consolidation efforts - Action News 5, January 31, 2019.
15. ^1 ^2 ^3 ^4 ^5 ^6 ^7Inside the 100K GPU xAI Colossus Cluster - Supermicro case study, December 2024.
16. ^1 ^2xAI announces expansion of supercomputer - KAIT8, December 4, 2024.
17. ^TVA approves providing power to xAI facility - Action News 5, November 7, 2024.
18. ^1 ^2 ^3Elon Musk's xAI to pull about half of its smog-belching turbines powering Colossus - The Register, May 8, 2025.
19. ^1 ^2xAI deploys 168 Tesla Megapacks to power its Colossus supercomputer in Memphis - DataCenterDynamics, May 22, 2025.
20. ^1 ^2SpaceXAI to restart work on wastewater treatment facility to serve Memphis data centers by Q1 2027 - DataCenterDynamics, June 23, 2026.
21. ^Musk to expand xAI's training capacity to a monstrous 2 gigawatts with third building at Memphis site - Tom's Hardware, December 31, 2025.
22. ^1 ^2 ^3 ^4NAACP sues Elon Musk's xAI over Memphis data center air pollution - CNBC, April 14, 2026.
23. ^Elon Musk says xAI will increase data center capacity 7x by 2027 - Tom's Hardware, August 13, 2026.
24. ^1 ^2Elon Musk's SpaceXAI to add another 660,000 AI GPUs this year, nearing a total of 1.44 million in operation - Tom's Hardware, September 25, 2026.
25. ^Anthropic will pay xAI $1.25B per month for compute - TechCrunch, May 20, 2026.
26. ^Musk says SpaceX agreed only six-month Colossus AI lease to Anthropic - Reuters (via Yahoo Finance), May 28, 2026.
27. ^SpaceX acquires xAI in record-setting deal as Musk looks to unify AI and space ambitions - Reuters (via The Standard), February 3, 2026.
28. ^1 ^2SpaceX blasts off with a record-breaking $75 billion IPO - NPR, June 11, 2026.
29. ^1 ^2A billionaire, an AI supercomputer, toxic emissions and a Memphis community that did nothing wrong - Tennessee Lookout, July 7, 2025.
30. ^In South Memphis, Elon Musk's Colossus Operated Gas Turbines Without Appropriate Permits, Residents and Activists Claim - Inside Climate News, July 17, 2025.
31. ^Shelby Co. Air Pollution Control Board denies appeal over xAI's turbine use, citing 'mootness' - Action News 5, December 15, 2025.
32. ^1 ^2 ^3State sets dates to retire temporary xAI turbines but allows some to go past original deadline - Mississippi Today, July 31, 2026.
33. ^1 ^2 ^3Illegal Pollution from Data Center Power Plants Shouldn't Harm Our Communities. We're Suing xAI. - Earthjustice.
34. ^Mississippi Permit Board Grants xAI's Request for 41 Southaven Gas Turbines to Power Memphis Data Center - Mississippi Free Press, March 10, 2026.
35. ^NAACP Asks Court for Emergency Action to Stop Illegal Air Pollution from xAI's Data Center Power Plant - Earthjustice, May 6, 2026.
36. ^Department of Justice sides with Elon Musk's xAI in Southaven lawsuit - Mississippi Today, June 16, 2026.
37. ^1 ^2Southaven residents sue Elon Musk's xAI alleging harm from gas turbines - Mississippi Today, June 9, 2026.
38. ^1 ^2State to hold permit hearing for xAI turbines in Southaven, EPA updates rules on temporary generators - Mississippi Today, February 9, 2026.
39. ^New Source Performance Standards Review for Stationary Combustion Turbines and Stationary Gas Turbines; Final Rule - Federal Register (U.S. Environmental Protection Agency), January 15, 2026.
40. ^Memphis residents file noise complaint against Elon Musk's xAI - Action News 5, September 25, 2026.