Nebius Longcross UK Cluster

Deep dive: How Nebius and Nscale build GPU clouds

Also known as Nebius UK Blackwell Ultra cluster; Nebius Ark Longcross

Operated by Nebius at Ark Longcross Park (Nebius UK site) .

Phase 1 seed dataset, compiled by hand. These rows were built from public operator, laboratory and vendor sources. A mechanical second-reader pass has since fetched every cited source: 1092 of 1153 systems have a readable citation that names them, and 40 are genuinely weakly sourced. Every claim carries its source and a confidence tier. Treat anything below verified as a lead, not a citation.

Measured performance

Rmax: -
Rpeak: -
Rmax ÷ Rpeak: -
Cores: -
Power: -
Per watt: - GF/W

Figures are as last publicly reported for the configuration described below, not a live measurement. Where a system was upgraded in place, the post-upgrade configuration is shown and the earlier one appears in the timeline.

What this machine is made of

One row per supplier relationship. “Supplier at build” is the company that shipped the part at the time; where that company has since been acquired, the parent it rolls up to today is shown beside it. That distinction is what makes ticker-level aggregation possible across a thirty-year dataset.

Role	Part	Supplier at build	Quantity	Confidence	Source
Integrator	- Nebius operates the cluster in Ark Data Centres' Longcross Park campus	Nebius NBISNASDAQ	-	Reported	techerati.com nebius.com
Accelerator	- 4,000 NVIDIA Blackwell Ultra (HGX B300) GPUs in the first phase, growing to about 9,000	NVIDIA NVDANASDAQ	4,000 reported	Reported	techerati.com nebius.com
Interconnect	- NVIDIA Quantum-X800 InfiniBand networking	NVIDIA NVDANASDAQ	-	Reported	nebius.com

AI datacenter metrics

Figures beyond an accelerator count, each with who stated it. What can and cannot be compared across AI datacenters.

Metric	Value	As of	Basis	Note	Source
Accelerators	4,000 accelerators	2025-11	Operator stated	4,000 Blackwell Ultra GPUs in the first phase as reported by Techerati for the Nebius launch; about 9,000 at full project scale.	techerati.com nebius.com

The read

Nebius's first UK deployment of NVIDIA Blackwell Ultra GPUs, hosted in Ark Data Centres' Longcross Park campus in Chertsey, Surrey and unveiled on 6 November 2025 after a June 2025 announcement. Techerati reports 4,000 B300 GPUs in the first phase growing to about 9,000, at a site that totals 54 MW across two Ark data centres (a site figure, not Nebius's cluster). Nebius's own November 2025 page names Blackwell Ultra and Quantum-X800 InfiniBand networking but the fetched version gives neither a count nor the site name, so the count rests on trade press and the tier is reported. A 16 MW cluster figure appears in coverage that could not be fetched, so no power figure is recorded. No FLOPS or HPL figure has been published.

Timeline

2025-06 Announced source
2025-11 First operational source

Site & facility

Ark Longcross Park (Nebius UK site)

Location: Chertsey, Surrey, United Kingdom
Commissioned: 2025

techerati.com nebius.com

Change history

2026-10-04 Added Nebius Longcross UK Cluster (Nebius)

Source check

We fetched this system's own citations and recorded whether each page actually mentions it. This is a corroboration signal, not a fact check, and it is published so you can see how well the sourcing holds up rather than take it on trust.

Cited source	Result	Found on the page
nebius.com	names system only	-
techerati.com	could not be fetched	-

Checked 2026-10-09 by pnpm verify. Re-run it and the table changes with the web.