Anthropic’s amended S-1 of 10 November gives its underwriters an option on “up to an additional 123,750,000 shares” for 30 days after the prospectus date. At the $74 midpoint of the $70 to $78 range, that is $9.16 billion of extra stock, by our arithmetic, or 15% on top of the 825 million shares offered.
The banks would buy those shares “at the initial public offering price less the underwriting discount”. SpaceX’s final prospectus in June said the reverse for its option: “The underwriters will not receive any discount or commission on any shares of our Class A common stock sold pursuant to the over-allotment option”.
Business Pill · IPO Float
A short explainer on IPO float, the share of a company sold in its listing. It teaches the general idea and does not discuss Anthropic’s over-allotment option.
The key insight: As we read it, the option is a short-term balancing tool: it lets Morgan Stanley oversell the deal by up to 15% and then either take the extra shares from Anthropic or buy them back in the market, depending on where the stock trades. What differs from SpaceX is the price of using it: Anthropic’s filing has the banks buy option shares less the underwriting discount, while SpaceX’s paid no discount on them.
The S-1/A says the underwriters “may exercise this option solely for the purpose of covering over-allotments”. In plain terms, the banks can sell more shares than the 825 million in the base deal, and the option is how they get the extra shares from Anthropic.
Morgan Stanley is named as the stabilization agent. The filing says “the underwriter may sell more shares of Class A common stock than the underwriters are obligated to purchase under the underwriting agreement, creating a short position”, and that “A short sale is covered if the short position is no greater than the number of shares available for purchase under the underwriter’s option to purchase additional shares”.
That short can be closed in two ways, the filing says: by exercising the option or by buying in the market. The bank “will consider, among other things, the open market price of our Class A common stock compared to the price available under the underwriter’s option to purchase additional shares”. Any short beyond the option is a “naked short position” that must be closed in the open market.
The over-allotment option in Anthropic’s S-1/A of 10 November and in SpaceX’s June prospectus, on a 30-day calendar from the prospectus date. Anthropic’s dates are expected, per its IPO site; the 18 December end date assumes an 18 November prospectus date. Dollar values and the 15% ratios are our arithmetic.
The Money at Each Price
At $70 the 123.75 million option shares come to $8.66 billion, at $74 to $9.16 billion and at $78 to $9.65 billion, by our arithmetic. The base deal of 825 million shares is $61.05 billion at $74, so a full exercise would take the public offering to $70.21 billion at the midpoint, by our arithmetic.
Anthropic’s own figures show the effect on its cash. The filing puts net proceeds from the offering and the $26.0 billion placement at “approximately $84.6 billion (or approximately $93.7 billion if the underwriters’ option to purchase additional shares of our Class A common stock is exercised in full)” at $74. The gap is $9.1 billion, by our arithmetic.
How It Compares With SpaceX
SpaceX’s option was the same size relative to its deal: 83,333,333 extra shares on 555,555,555, or 15%, by our arithmetic. Its prospectus shows underwriting fees of $500,000,000 with or without the option, and a per-share fee of $0.90 on base shares and $0.00 on option shares. Morgan Stanley was its stabilization agent too.
SpaceX’s option was used in full. Its third-quarter 10-Q says it sold “638.9 million shares of its Class A common stock at a public offering price of $ 135.00 per share, including the full exercise of the underwriters’ over-allotment option”. That is 555,555,555 plus 83,333,333 shares, or $11.25 billion of option stock, by our arithmetic.
Anthropic’s fee table, which the filing says shows amounts “assuming both no exercise and full exercise” of the option, is still blank. Our retail-allocation piece derived an implied fee of about 1.04% of the offer price from the filing’s $793 million-per-dollar figure. At that rate the option shares would carry about $95 million of fees at $74, by our arithmetic, against $0 on SpaceX’s option.
Where It Sits in the Calendar
Anthropic’s IPO site says “the final IPO share price is expected to be set on November 18th (EST), and shares are expected to begin publicly trading on November 19th (EST)”. If the prospectus is dated 18 November, the 30-day option window runs to 18 December, by our arithmetic. Our day-by-day timeline covers the steps before that, and the lock-up calendar the releases after it.
At our EDGAR check at about 19:05 UTC on 11 November, the 10 November S-1/A was still Anthropic’s latest filing; no final prospectus had been filed.
The Structural Read
As we read the cash side, a full exercise is worth about $9.1 billion of extra net proceeds to Anthropic on its own figures, $84.6 billion against $93.7 billion at $74, by our arithmetic.
As we read the precedent, SpaceX’s same-sized option was used in full, according to its 10-Q; whether Anthropic’s is used depends on how the stock trades in the 30 days after pricing, as the filing describes.
Anthropic, PBC, Form S-1/A Amendment No. 2, 10 November 2026
“The underwriters may exercise this option solely for the purpose of covering over-allotments, if any, made in connection with the offering of the shares of common stock offered by this prospectus.”
Three Implications
FOR IPO BUYERS The filing says Morgan Stanley, as stabilization agent, may buy shares in the market to stabilize the price and may end those activities at any time.
FOR ANTHROPIC The filing puts net proceeds at about $84.6 billion, or about $93.7 billion if the option is exercised in full, at the $74 midpoint.
FOR THE BANKS The option shares are bought at the IPO price less the underwriting discount; the fee table in the S-1/A, with and without the option, is still blank.
The framework records: “the capex race is no longer a corporate spending cycle. It is a sovereign-scale financing problem dressed in tech-company clothing”.
As we read it, the over-allotment option is one more line in that financing: up to $9.1 billion of extra net proceeds on Anthropic’s own figures, decided by the banks within 30 days of pricing. The framework predates the IPO and does not discuss the option.
What Is Not Established
The fee rate is not stated: the 1.04% is our estimate from a rounded filing figure, and could be anywhere from about 0.98% to 1.10%. The final price, the number of shares sold and whether the banks use the option at all will only be known after pricing; nothing in the filing commits them to exercise it.
The filing does not say why its option terms differ from SpaceX’s. We did not contact Anthropic or its underwriters for this piece. Where retail buyers can take part is in our countries piece.
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Anthropic’s underwriters hold a 30-day option on 123.75 million more shares, $9.16 billion at the $74 midpoint by our arithmetic, priced at the IPO price less the underwriting discount. SpaceX’s same-sized option in June carried no discount, and its 10-Q shows it was exercised in full.
A note on sourcing. The option terms, the stabilization language and the proceeds figures are from Anthropic’s S-1/A No. 2, filed with the SEC on 10 November 2026, which we read in full. SpaceX’s terms are from its final prospectus filed on 12 June 2026 and its third-quarter 10-Q. The expected pricing and trading dates are from Anthropic’s IPO site. The 1.04% fee rate is our earlier estimate from the filing’s rounded proceeds figures, not a number Anthropic has stated; dollar values, ratios and dates are our arithmetic. We did not contact Anthropic or its underwriters for this piece.
Gennaro Cuofano is a CRO and tech executive who has worked in AI since late 2015, starting with bringing NLP, natural-language generation, voice and chatbot products to the marketing industry. His background is in law and finance: he holds a Master's degree in Law and an International MBA with an emphasis on corporate finance (LUISS Business School and the University of San Diego, 2012), and worked as a financial analyst at a real-estate investment firm in San Diego and as an assistant controller. His work focuses on business model strategy, business engineering and, more broadly, structural analysis: how companies make money, read from their own filings. He created FourWeekMBA and leads research there and at The Business Engineer, his newsletter on AI and business strategy, with over 95,000 subscribers and more than 1,000 published analyses. His writing has also appeared on Entrepreneur (for example, How to Digitize a Family Business in Europe) and HackerNoon. Find him on LinkedIn and Substack. See how we source.
