Anthropic Is SpaceX's Largest Customer: The Filings

§ 01What SpaceX disclosed#

SpaceX booked $14.575 billion of revenue in the third quarter of 2026, up 161% from $5.576 billion a year earlier. Most of the jump came from one segment. Super Intelligence, the former AI segment that holds Grok, Cursor, X and the company’s data center business, went from $813 million to $7.56 billion, about 9.3 times. Inside it, the line called SI Solutions & Infrastructure rose from $359 million to $7.022 billion.

The customer table sits in the revenue note. Two customers each passed 10% of revenue. The filing says “revenue from Customer A relates to all three segments and revenue from Customer B relates to the SI segment.” A year earlier, Customer B was below the 10% line and is not shown.

The same note adds that one customer accounted for 27.7% of SpaceX’s accounts receivable on September 30, 2026, against none above 10% at the end of 2025. The filing does not say which customer that is.

§ 02How big Customer B is in dollars#

The 10-Q gives percentages, not dollar amounts. Applying them to the reported totals gives a rough size (our arithmetic, from percentages rounded to one decimal):

• Third quarter: 34.5% of $14.575 billion is about $5.03 billion. That is roughly two-thirds of the Super Intelligence segment’s $7.56 billion.
• Nine months: 24.2% of $27.083 billion is about $6.55 billion, which implies about $1.5 billion before July.
• Customer A: 16.6% of the quarter is about $2.4 billion, spread across launch, Starlink and AI.

So in one quarter, a single AI customer went from too small to list to more than a third of a company that also runs Starlink and its launch business.

§ 03What Anthropic agreed to buy#

The S-1, filed on October 26, sets out the terms on Anthropic’s side. Between May and October 2026, Anthropic entered into and amended several agreements with SpaceX.AI LLC, formerly X.AI LLC, a wholly owned SpaceX subsidiary. The filing calls them the SpaceXAI Arrangements.

• Size: “an aggregate of up to $120.5 billion over terms extending into 2029”.
• Run rate: about $3.1 billion a month once all capacity has been delivered, which Anthropic expects in December 2026, with different fees while capacity ramps.
• Exit: after initial non-cancelable periods ending in January 2027 and March 2027, “each agreement may be cancelled by either party upon 90 days’ advance written notice.”

At the full rate, $3.1 billion a month is $9.3 billion a quarter. That is more than Starlink’s entire Connectivity segment earned in the third quarter ($5.248 billion), and about 64% of all SpaceX revenue in that quarter. The third-quarter figure was a ramping quarter, not the full rate.

§ 04What it costs SpaceX to serve#

SpaceX books these deals as cloud services. The 10-Q describes a “stand-ready promise to provide continuous access to reserved compute capacity”, paid as fixed monthly fees and recognized as capacity comes online.

The segment table shows the build behind it. In the third quarter, Super Intelligence earned $7.56 billion of revenue and $431 million of operating income, against $2.675 billion of cost of revenue and $2.473 billion of depreciation and amortization. Its capital spending was $16.444 billion in the quarter, out of $19.593 billion for all of SpaceX. Over nine months the segment still shows an operating loss of $3.295 billion. The quarter the reserved-capacity line ramped is the quarter the segment showed an operating profit.

§ 05Anthropic’s other compute suppliers#

SpaceX is one supplier among several. The same S-1 describes Claude on “all three major cloud platforms”, Amazon Web Services, Google Cloud and Microsoft Azure; a 2026 lease arrangement with Broadcom for specialized AI accelerators; and data centers run for Anthropic by Fluidstack. Our earlier record of the Anthropic S-1 covers those commitments, and the prospectus walkthrough covers the revenue side.

What makes SpaceX stand out is speed and size. The arrangements were signed between May and October, the capacity is due in full by December, and in its first big quarter the contract already made Anthropic SpaceX’s top customer, ahead of Customer A, whose revenue spans all three segments.

§ 06What is confirmed and what is not#

• Confirmed by SpaceX’s 10-Q: a customer at 34.5% of third-quarter revenue, all in Super Intelligence, and the cloud services accounting.
• Confirmed by Anthropic’s S-1: the SpaceXAI Arrangements, up to $120.5 billion, about $3.1 billion a month from December 2026, and the 90-day exit after early 2027.
• Reported by Bloomberg, one unnamed source: that Customer B is Anthropic. Neither filing makes that match.
• Not disclosed: which data centers serve Anthropic, and how much of Claude’s traffic runs on SpaceX capacity.

The story spread on X within the hour, through Kalshi, Andrew Curran and Polymarket.

§ 07What it means for teams that build on Claude#

CellCog’s AI employees run on Claude Opus 5.5, so we read this one closely. For anyone building on Claude, the filings point to two things. First, Anthropic is buying capacity fast and from more than one place, which is what keeps a frontier model available as demand grows. Second, the SpaceX capacity is large but not locked in: from early 2027 either side can leave on 90 days’ notice. A team that depends on one model gains more from that spread of suppliers than from any single contract.