spacex's customer b: what both filings say about the anthropic deal
on october 29, 2026, bloomberg reported that anthropic is spacex's largest customer. most coverage stopped at the headline. both companies have now filed with the sec, so you can read both sides of the same deal. here they are, next to each other.
"customer b" was 34.5% of spacex's total q3 2026 revenue, about $5.0 billion, all of it in spacex's ai segment. neither filing names the customer; bloomberg reported it is anthropic. anthropic's own s-1/a confirms up to $120.5 billion of compute from spacexai, about $3.1 billion a month at full capacity, cancelable on 90 days' notice after early 2027.
what spacex's 10-q says
one customer went from below the 10% disclosure line to a third of the company's revenue in a year. figures from spacex's form 10-q for the quarter ended september 30, 2026 (sec edgar), in millions of dollars unless marked.
| line | q3 2026 | q3 2025 |
|---|---|---|
| total revenue | $14,575 | $5,576 |
| si (ai) segment revenue | $7,560 | $813 |
| of which si solutions & infrastructure | $7,022 | $359 |
| customer b, share of total revenue | 34.5% | under 10%, not disclosed |
| customer a, share of total revenue | 16.6% | 23.9% |
for the first nine months of 2026, customer b was 24.2% of revenue. the 10-q says customer b's revenue relates to the si segment, while customer a's spans all three segments, and that no other customer was above 10% (spacex 10-q, q3 2026).
what anthropic's s-1/a says
anthropic describes the other side of what looks like the same contract, in more detail than spacex does. from its s-1/a filed november 2, 2026 (sec edgar):
- it entered agreements with spacexai to access compute powered by nvidia gpus.
- it agreed to spend an aggregate of up to $120.5 billion over terms extending into 2029.
- that works out to about $3.1 billion a month once all capacity is delivered, which it expects in december 2026, with different fees during ramp-up.
- after initial non-cancelable periods ending in january and march 2027, either party can cancel each agreement on 90 days' written notice.
side by side
| question | spacex 10-q | anthropic s-1/a |
|---|---|---|
| who is the customer? | "customer b", unnamed | names spacexai as a compute provider; no customer label |
| how big? | 34.5% of q3 revenue, about $5.0b | up to $120.5b into 2029 |
| what is it for? | sits in the si segment | nvidia gpu compute |
| run rate | about $1.7b a month in q3, by my arithmetic | about $3.1b a month at full capacity, expected december 2026 |
| can it end? | not addressed in the concentration note | yes, 90 days' notice by either party after jan and mar 2027 |
the identification rests on bloomberg's source, as reported by seeking alpha (oct 29, 2026). the two filings are consistent with it: one describes a single ai customer in the si segment; the other describes a single ai compute contract with spacexai. neither company has put the name in writing.
the arithmetic nobody ran
if the contract ramps to the rate anthropic describes, it is bigger than the q3 number suggests. 34.5% of $14.575 billion is about $5.0 billion for the quarter, or about $1.7 billion a month. anthropic's filing puts full capacity at about $3.1 billion a month, roughly $9.3 billion a quarter.
rough arithmetic, not a forecast: hold spacex's other q3 revenue flat at about $9.5 billion, add a fully ramped $9.3 billion, and one customer would be close to half the company's quarterly revenue. revenue recognition, ramp fees, and every other line will move, so treat that as an order of magnitude. the point is the direction.
why both sides are exposed
spacex depends on one ai customer; anthropic depends on whoever has compute. spacex owns xai, the maker of grok, following its acquisition of musk's xai business (seeking alpha, oct 29 2026). so the company behind claude is buying gpu capacity from the parent of a direct competitor.
anthropic's s-1/a addresses that kind of dependency directly. it says its access to compute is subject to its providers' allocation decisions, which can be shaped by capacity constraints, their own internal demand for compute, and their relationships with other ai companies (anthropic s-1/a, nov 2 2026). in this market, the competitors are each other's customers.
the lesson for a small business
if one client, brand, or platform is a third of your revenue, you are running spacex's risk without spacex's balance sheet. spacex can absorb a customer leaving on 90 days' notice with a $14.6 billion quarter behind it. a one-person business with one retainer at 35% of income cannot. the fix is boring: cap any single source at about a third, and know which one you would replace first. the same logic applies to the tools you run on, which is the subject of is it safe to build your business on claude?
for the full picture of anthropic's commitments, including the $895.4 billion total and why q3 swung to a gaap loss, see anthropic's $895 billion compute bill.
common questions
Who is SpaceX's Customer B?
SpaceX's 10-Q for the quarter ended September 30, 2026 does not name it. It lists Customer B at 34.5% of consolidated Q3 revenue, all of it in the Super Intelligence (SI) segment. Bloomberg, citing a person familiar with the matter, reported that Customer B is Anthropic. Anthropic's S-1/A confirms it buys compute from SpaceXAI but does not use the Customer B label.
How much does Anthropic pay SpaceX?
Anthropic's S-1/A says it agreed to spend up to $120.5 billion with SpaceXAI over terms extending into 2029, about $3.1 billion a month once all capacity is delivered, which it expects in December 2026. On SpaceX's side, 34.5% of $14.575 billion in Q3 revenue is about $5.0 billion for the quarter.
Can Anthropic cancel its SpaceX compute contract?
Yes, after a point. Per Anthropic's S-1/A, after initial non-cancelable periods ending in January 2027 and March 2027 under the respective agreements, either party may cancel each agreement on 90 days' advance written notice.
How big is SpaceX's AI business?
SpaceX's SI segment reported $7.56 billion of revenue in Q3 2026, up from $813 million in Q3 2025, out of total company revenue of $14.575 billion. SI Solutions & Infrastructure alone was $7.022 billion, up from $359 million.
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