Good day. Today, we have a fascinating look into what it actually takes to build the infrastructure required to fuel the global AI arms race. Elon Musk’s datacenters have taken over a 114-acre tract of land on the Mississippi-Tennessee border, near Memphis. Another million-square-foot datacenter is under construction just north of the Tennessee border.

But Memphis is the front line of Musk’s costly foray into the AI wars. His artificial intelligence company, xAI, has already built one massive data center here in the Bluff City that it calls the world’s largest supercomputer. That facility, called “Colossus,” houses over 200,000 Nvidia chips and powers the technology behind the AI chatbot Grok. Now, Musk is close to finishing the second facility, which will be even bigger. He calls it Colossus 2.

Musk, who has been at the forefront of innovation in electric vehicles, rockets and brain-computer interfaces, is in the unusual position of playing catch-up to rivals like Sam Altman’s OpenAI.

Finishing Colossus 2 will cost tens of billions of dollars, some AI and data center experts say. The Nvidia chips alone cost a fortune: Musk will need to spend at least $18 billion for the roughly 300,000 more chips he needs to complete the Memphis project, a person familiar with the project’s financials said. Musk said in July that Colossus 2 will have a total of 550,000 chips and has separately signaled it could eventually have a million processing units.

Read our deep dive into what’s happening in Memphis here.

Also today:

• Pentagon pulls back on cyber training.
• LinkedIn sues alleged data scrapers.
• Hackers claim 1 billion Salesforce records stolen.

After declining more than 6% last week, Lumen Technologies finished the week of October 3 up more than 13.5%. The stock was the only security to climb more than 7%.

Commvault Systems fell 6.43% for the week. It was one of six stocks that registered losses this week.

Collectively, the CyberIndex fell nearly 3% since Monday, despite gains between 1% and 3% for each of the top three firms by market cap in the measure.

-- Jon Leckie

The index looks at the top 20 cyber companies by market capitalization. The latest group: Akamai, Check Point, Cisco, Cloudflare, Commvault, CrowdStrike, Cyberark, F5, Fortinet, Leidos, Lumen, Okta, Palo Alto Networks, Qualys, Rubrik, SailPoint, SentinelOne, Tenable, Varonis, Zscaler.

Discord Says Vendor Breach Exposed Sensitive Data. Discord disclosed that a third-party customer service vendor was compromised, allowing unauthorized access to a limited number of user-submitted government ID images used for account verification. The company said fewer than 1% of users were affected, and that it revoked the vendor’s access and is notifying impacted customers. (Eurogamer)

The WSJ Pro Cybersecurity team is Deputy Bureau Chief Kim S. Nash and reporters Angus Loten, James Rundle and Catherine Stupp. Follow us on X @WSJCyber. Reach the team by replying to any newsletter you receive or by emailing Kim at kim.nash@wsj.com.