Learnings from our Anthropic clients and the S-1

The Prospero Wealth advisors huddled together today to discuss the highlights of the planning we’re doing for our Anthropic clients. 

What quickly became apparent is how varied the planning considerations have been for every individual we’ve worked with at Anthropic (whether as a client or prospect). Timing, role, equity types, and personal aspirations all have required the exploration of vastly different planning approaches. 

While being cognizant of that, a few commonalities of the Anthropic IPO are worth covering:

1. BEWARE: The S-1 published on October 26, 2026 is still preliminary. It has many areas that are still blank. Pricing, withholding, and lock-up percentages are subject to the final prospectus.

2. Most (all?) vested RSU holders will face a large tax bill for this year, some of which will come before employees have access to sell most of their shares.

   • Vested RSUs will be taxable at the day of the IPO listing and will count as ordinary income for 2026.

   • Withholdings may fall short. Anthropic will withhold shares at a single assumed flat rate (the rate is blank in the S-1 filing). For high earners, especially in California, that rate is unlikely to cover the full tax due (and in fact, may lead to underpayment penalties due to a failure to meet safe harbor requirements). Employees should expect additional balance due and should look at making estimated payments in many cases to avoid possible penalties. Knowing and setting their withholding rate correctly is important.

   • DO NOT FORGET that the IPO is only one liquidity event for Anthropic 2026. Many employees have also participated in tender offers that will impact expect taxation here.

3. You need to know your own liquidity calendar.

   • There are at least 3 groups called out in the S-1 (beyond the 7 co-founders) with differing staged releases prior to standard 180 day lock-up. As an employee, it’s important you know what your own liquidity calendar lays out like. As of right now, there are still blanks left in the S-1 in this area when defining the various groups of shareholders.

4. Many of the usual concentrated wealth solutions are not available to employee shareholders. The insider trading policy does not allow for collars, pre-paid variable forwards, equity swaps, margin accounts and pledging shares as collateral (with some limited exceptions).

   • Examples of other diversification strategies that ARE allowed include:

     • Scheduled sales, including 10b5-1 plans (can be put into place during lockup but most start after lockup).

     • Charitable giving (see below)

     • Tax-managed portfolios, such as direct-indexing that harvests losses to offset gains from selling

5. Charitable giving is a major opportunity for many Anthropic Insiders. 

   • The matching plan. Employees can pledge part of their equity, or cash from selling it, to a donor-advised fund or other nonprofit. Anthropic matches with Class N shares or cash. The plan is already heavily used: Anthropic booked a $2.0B expense in Q3 for donations employees made in August 2026.

   • Why the IPO year? That’s when income spikes, so it’s the year to model giving low-basis shares to a DAF. Have their CPA run the numbers under 2026 rules, including the AGI limits.

     • State deductibility of charitable contributions may vary by state.

6. The governance of Anthropic is fairly unique, which alters its risk profile. Anthropic is a public benefit corporation and its Long-Term Benefit Trust elects most of the board. This Trust does not have profit as its only goal. 

Anthropic employees appear to be at the precipice of one of the largest IPOs ever. The late-year timing of the IPO, along with the fairly unique governance profile, adds significant complexity to the employees trying to manage this in the middle of a business that is essentially scaling vertically. 

We believe it's really important for employees to be proactive about their own financial plans and needs during this once-in-a-lifetime event.