Serotonin review: a $30,000-a-month retainer, 73 client names and no published price

Serotonin is the agency Amanda Cassatt founded after three years as chief marketing officer of ConsenSys, and for most of its life it has been the name Ethereum-era protocols hired when they wanted a launch run by people who had already done one. It publishes no price, no client terms and no case study, and nobody has reviewed it on Clutch or Trustpilot. The one hard number in the public record arrived by way of securities law: a consulting agreement filed with the SEC by Bit Digital, a Nasdaq-listed company that pays Serotonin $30,000 a month for “Narrative and Thesis Development for Ethereum”, social media and PR. It was signed one week before Bit Digital announced it was turning itself into an Ethereum treasury company, and it is still running ten months after Cassatt joined Bit Digital’s board. Our score is 7/10.

We read serotonin.co on 3 November 2026: all nine pages, the se.ro platform terms and privacy policy, and the intake form behind the Contact button. We also read the site as it stood in 2021, 2023, 2024 and early 2025, the Bit Digital filings that contain the agreement and its payments, Decrypt’s reporting on the two companies spun out of Serotonin’s product studio, the sites of Mojito, Franklin and Spindl, Wiley’s page for Cassatt’s book, the Built In profile, the Lever job board, Clutch and Trustpilot. Every figure below comes from one of those.

Who is behind Serotonin

Two founding dates circulate, both from Serotonin. The biography Bit Digital filed for its new director says Cassatt has been “Co-Founder and Chief Executive Officer, since July 2019, of Serotonin Inc,. a services company for institutions and startups in the blockchain and crypto industry”, July 2019 being the month she left ConsenSys, where she had been chief marketing officer since August 2016. The Built In profile says “Year Founded: 2020”. The earliest copy of serotonin.co we can find, from 19 February 2021, described “a marketing firm and product studio for transformative technologies” and listed two founders: Cassatt as “Co-founder and CEO” and Matthew Iles as “Co-founder and Partner”. Iles was still on the team page in February 2023 and gone by February 2024, when Elise Ransom appears as Managing Partner. The site does not record his departure; today’s team page calls Cassatt “Founder & CEO”, singular.

The legal structure is two entities. The se.ro terms are issued by “Serotonin Inc. and Serotonin Holdings LLC”; the Bit Digital agreement is signed by “Serotonin Inc., a Delaware Corporation” at 31 Hudson Yards, Floor 11, New York, with legal notices routed to a Middletown, Delaware mailbox. A Delaware corporation files nothing a buyer can read, so unlike Wachsman’s Irish and UK companies there are no accounts or director lists to check.

The team page holds 42 cards; two say “We’re Hiring!” and two people appear twice, leaving 38 names. At the top are Cassatt, AJ Banon as General Partner, Ransom as Managing Partner, two further partners, Teddy Ellison as Legal Services Managing Partner, heads of recruiting and product, and Patryk Krasnicki as Director of Research. Below them: a senior PR director, Ryleigh Ebron, who was on the May 2022 page as PR manager, two senior PR managers, content, social and growth staff, a director of finance and, unusually for a PR firm, three engineers, a founding product designer and an “AI Associate”. The archived pages carry about 43 people in May 2022, 42 in February 2023 and 39 in February 2024; Serotonin has neither grown nor shrunk through a full crypto cycle. Built In lists it as fully remote; the Lever board has two openings, an AI infrastructure engineer and a “Pitch Yourself” post.

What has changed is the description. In 2021 it was a marketing firm and product studio; by February 2024, “the leading web3 marketing and product studio”. Between October 2024 and January 2025 that site was replaced by a sparse single page whose only sentence is “Bringing the world’s breakthrough technologies to market”, described in its page metadata as “a go-to-market platform for web3, AI, and biotech. You build the future, we do the strategy, recruiting, and legal work.” The word “agency” survives in the marketing page’s title alone. Cassatt’s profile has moved the same way: a Wiley handbook, Web3 Marketing, published in April 2023, a podcast called Endgame, and since this year a public-company board seat.

What Serotonin sells

Seven things, each in one paragraph. Marketing: “comprehensive marketing services across all major channels to deliver measurable results globally.” Strategy: “a tailored strategy spanning product, marketing, and brand positioning.” Research reports on “the evolving onchain economy”. Recruiting. Legal: “Business & Compliance Services” for “startups and VC firms, from formation through growth stages, including compliance, fundraising, and M&As”. Products: three software companies. And se.ro, a members’ platform offering “One view for every conference, hackathon, summit, and side event” and a research feed “hand-selected by humans who track the industry full-time”. The 2023 marketing page was more specific: eight lines from brand and positioning to growth and analytics, a PR team that “consistently places our partners in the top trade publications and leading industry podcasts”, and named work for “Proof, Doodles, Decentraland, World of Women, and Sotheby’s”. Of those five, only Sotheby’s is on the clients page today.

The only itemised scope of work in the public record is Exhibit A of the Bit Digital agreement, and it is a plain earned-media retainer: “Narrative and Thesis Development for Ethereum”; “Social Media Strategy and Execution” for “Sam Tabar’s X Account” and “Bit Digital’s X Account”, Tabar being Bit Digital’s chief executive; and “PR Strategy and Execution” broken into podcasts, speaking opportunities, commentary, “TV and Broadcast pitching” and “Op-eds and thought leadership”. No wire, no paid media, no article count, no KOL programme. The desks that sell those are in our PR distribution comparison.

The products page needs reading twice. Mojito and Franklin are documented spinouts, covered below. The third entry, “Spindl (Coinbase)”, is described as “the leading web3 marketing analytics platform, built by the team behind Facebook’s original ad product”. Spindl’s own site and blog belong to Antonio García Martínez; its homepage places Serotonin in the “Trusted by top Web3 companies” strip as a customer, and its blog records a Serotonin partnership in July 2023 and, later, “Spindl is joining Coinbase”. Serotonin does not say it built Spindl, but filing a customer relationship under the same heading as two companies it incubated invites a reading the facts do not support. One more note: se.ro is the only product with published terms, under which “All paid membership subscriptions for the Services are non-refundable unless otherwise specified in writing from us” and disputes go to individual arbitration with a class-action waiver.

Pricing in 2026

There is no price on serotonin.co, no starting figure and no band. The Contact button opens a Typeform titled “Serotonin Services Intake” that asks which services you want, for “a short description about your project”, “What is your monthly budget?” as an open text field, how you heard about Serotonin, and for a calendar link. That is less than Wachsman or Lunar Strategy disclose, whose forms at least show the bands they expect.

The figure that exists is in Exhibit A of the agreement Bit Digital filed on 12 December 2025: “Cash Fee: $30,000 Monthly Retainer”, plus third-party expenses “at cost” if approved in writing. The payment terms are Serotonin’s own, since the document is headed “SEROTONIN INC. CONSULTING AGREEMENT”: “Client will be invoiced monthly in advance, on or before the first day of each month”, work starts only after the first payment clears, a delay of more than five days carries “a penalty fee of the lesser of (i) 1.5% per month or (ii) the highest rate permitted by applicable law”, and after ten days Serotonin “shall be permitted to cease providing services until payment is received in full”. Bit Digital’s 2026 shareholder-meeting statement puts the 2025 total at $207,143 in “consulting fees to Serotonin Inc.” for a contract that began on 18 June; its quarterly report filed on 13 August 2026 still says “The Company pays Serotonin a monthly cash retainer of $30,000”. One client is worth at least $360,000 a year to the agency.

Two cautions before treating $30,000 as the price. It is one contract, approved by a board on which the agency’s founder now sits; a startup filling in the intake form may be quoted above or below it. And it buys a scope with no numbers in it: no placement count, no posting cadence, no deliverable list beyond the headings above. For orientation, Outset PR prints $8,000 to $16,000 a month with guaranteed feature counts, Wachsman’s form starts at $10,000, and Chainwire’s smallest release package is $1,399 in our Chainwire review. Serotonin’s one known price is the highest monthly figure in this series.

Clients and case studies, checked

The clients page is 73 names in capitals on a black background, each linked to the client’s own website: Alchemy, Arbitrum, Bain Capital Crypto, Bit Digital, BitGo, Chainlink, Circle, CoinDesk, Filecoin, Lido, Optimism, PayPal, Paxos, Polygon, Ripple, Robinhood, Sotheby’s, Starkware, TON Foundation, VanEck, Vogue, WisdomTree and Zcash among them. There are no logos, dates, scopes or results, and no case-study page exists. A link to a client’s homepage is a courtesy, not evidence.

Two names are confirmed by someone other than Serotonin. Bit Digital is confirmed in more detail than any client in this series, by scope, price and date, in its own filings. Sotheby’s is confirmed through Mojito: Decrypt reported on 21 October 2021 that Mojito, “an NFT commerce suite developed by Serotonin”, powered the new Sotheby’s Metaverse marketplace, that the auction house was among its investors, and that “Serotonin announced that Mojito has spun out of the firm, raising $20 million in funding at a $100 million valuation”. In April 2023 Decrypt reported the second spinout: Franklin, a crypto-and-fiat payroll company founded by Megan Knab, Serotonin’s former vice-president of finance, raising “a $2.9 million seed funding round led by venture capital firms gumi Cryptos Capital (gCC) and CMT Digital”. CMT Digital is on the clients page. The same article relays Serotonin’s claim that Mojito had generated more than $120 million in sales for clients including Sotheby’s and Pace Gallery; that is the agency’s figure, and we count it as a claim.

Cassatt described the model to Decrypt plainly. “Many Serotonin services clients naturally become customers of Mojito or Franklin,” she said. “Companies come to us for help with their Web3 strategies, then once it comes to executing that strategy, they need a software provider.” The relationships now run in several directions: Franklin’s homepage carries a testimonial from Serotonin’s director of finance, and Mojito’s partner page lists “CAA, Serotonin and Polygon” as agencies it works with rather than as a parent. The roster has turned over, too: of the 14 partner logos on the February 2021 homepage, seven remain in 2026. The Bit Digital agreement explains how the page is built: clause 8 grants Serotonin a revocable right “during the term of this Agreement” to publish the client’s name and logo “and a brief scope of services provided”. Read that way, the 73 names are more likely a current roster than a history, which makes it a better list than most, and still one with no result attached.

Third-party reviews (Clutch, G2, Trustpilot, Reddit) and what they actually mean

There are none. Trustpilot has no page for serotonin.co. Clutch, where Coinbound has 14 reviews and Solus 22, has no listing for this company; the only Serotonin on Clutch is a performance-marketing agency in Manchester, England, with no connection to it. G2 is for software and neither the agency nor se.ro appears there. Reddit mentions of the agency are job-board reposts of its vacancies and the Bit Digital board announcement; we found no thread in which a client describes the work. In six years no customer has said anything about Serotonin in a place a buyer can read.

What the record holds instead is coverage: Decrypt on both spinout rounds, a Wiley book endorsed by Pantera Capital’s chief investment officer and ShapeShift’s founder, and a biography in three SEC filings. That is a founder’s reputation, and a good one; it is not a client’s account of a campaign. The practical consequence is the same as for Wachsman: ask for three references with dates and scopes, and expect to get them, because an agency with 73 current names has no reason to refuse.

The terms (contract, refunds, governing law, exclusivity)

Serotonin publishes no client terms; the platform terms on its site govern se.ro members. For agency work the only public contract is the one Bit Digital filed, and because it is Serotonin’s own paper it is a fair guide to what a new client will be handed. Term: six months, then “automatically renewed for additional consecutive terms of six (6) months” unless either side gives written notice “at least thirty (30) days’ prior to the end of the Initial Term or any Renewal Term”. Termination for cause is drafted one way: “Consultant may terminate this Agreement or any statement of work, effective immediately upon written notice” if the client becomes insolvent. There is no clause under which the client can end the term early for poor work and no refund clause; on termination “for any reason” Serotonin is paid for work completed. Intellectual property is assigned to the client outright. Exclusivity is disclaimed: Serotonin “engages in work from time to time for other clients in the same industry, and this fact alone does not constitute a conflict”. Both sides accept a one-year mutual non-solicit of staff, and Serotonin may, “at the Contractor’s absolute discretion, engage a third-party sub-contractor to perform some or all of the obligations”. Governing law is New York; no arbitration forum is named. Signed as drafted, it commits you to six months at a time, paying ahead, with no exit for performance and no promise about who does the work.

The same filings describe the relationship around the contract. The agreement is dated 18 June 2025. On 25 June 2025 Bit Digital announced a “Strategic Shift to Ethereum Treasury and Staking Operations”, the narrative Serotonin had been hired to develop a week earlier. On 9 December 2025 its board elected Cassatt a director from 1 January 2026 and awarded “Mango Sticky Rice Limited, a Hong Kong entity controlled by Amanda Cassatt” restricted share units worth $200,000; the shareholder-meeting statement puts her 2025 total at $407,143, stock plus consulting fees, and renominated her in June 2026. Every report since repeats that “Amanda Cassatt, a director of the Company, is a principal of Serotonin and has an ownership interest in the entity”. Nothing here is undisclosed. But the agency’s only public reference client is one whose board its founder sits on, and the agency’s site, which lists Bit Digital among the 73, says nothing about the seat.

Serotonin against the desks and networks we already track

Serotonin sells what Wachsman sells, senior counsel and an earned-media desk on a monthly retainer, plus things Wachsman does not: research, recruiting, a compliance practice, engineers and a members’ platform. It is the second of the four long-standing crypto PR names in our Web3 marketing agencies ranking that publish no price, after Wachsman. Wachsman has a decade, four registered companies, a $25.4 million fee year in an independent table and zero client reviews. Serotonin has six years, two funded spinouts, one client whose contract is public to the dollar, and zero client reviews. The other retainers in our crypto PR agencies comparison sit below both on price where a price is known.

Agency	Published price	Clutch	Trustpilot	Client terms public	Our score
Serotonin	None (SEC exhibit: $30,000 a month)	No listing	No profile	One contract, via the SEC	7/10
Wachsman	None (form: $10,000+ a month)	Not yet reviewed	No profile	No	7/10
Coinbound	PR FAQ “$10,000 and $20,000”	5.0 (14)	3.2 (3)	Yes	7/10
MarketAcross	None (results-based retainer)	5.0 (9)	No profile	No	7/10
Solus Agency	None (Clutch min $50,000)	5.0 (22)	No profile	No	6.5/10
Chainwire	$1,399 to $10,799 per release	n/a	No reviews	Yes	6.5/10
Outset PR	$8,000 to $16,000 a month	5.0 (4)	No profile	Yes	6/10
Melrose PR	None	Not yet reviewed	No profile	No	6/10

If the brief is a token launch with paid placements, a KOL programme or a fixed number of articles, Serotonin is the wrong door; the wires in our PR distribution comparison start at $1,399 and the networks in our crypto ad networks ranking start at $100. If the brief is a narrative for a protocol, a listed company or a fund, with the founder’s social accounts, podcasts and op-eds run by people who did this for Ethereum itself, Serotonin is one of a handful of firms with that history, and the only one whose working contract you can read before the first call.

Verdict

Our score is 7/10, level with Wachsman, Coinbound and MarketAcross and above Chainwire’s 6.5. Serotonin earns the top of the range on substance: a founder who ran marketing for Ethereum’s largest company and wrote the Wiley textbook on the field, a 38-person team steady since 2022, two spinouts that raised $22.9 million from named investors, and a contract in the public record whose price, scope and terms we could read line by line, which no other agency in this series offers. It loses points on everything it chooses not to show: no price, no terms, no case study, no result attached to any of 73 names, no client review anywhere, a founding story with two dates and a vanished co-founder, a products page that borrows a Coinbase acquisition it did not make, and a contract whose only public example is with a company where the founder is now a paid director. The $30,000 month is real; so is the fact that the only party to have publicly vouched for it is a board that includes the agency’s founder.

Serotonin FAQ

How much does Serotonin cost?

Serotonin publishes no prices, and its intake form asks for your monthly budget as free text. The only figure on record is the $30,000 monthly retainer in the consulting agreement Bit Digital filed with the SEC in December 2025, for Ethereum narrative work, two X accounts and PR, invoiced monthly in advance. Treat it as one data point for a listed-company client, not as a rate card.

Who owns Serotonin?

Founder and chief executive Amanda Cassatt, through Serotonin Inc., a Delaware corporation, and Serotonin Holdings LLC. Bit Digital’s filings describe her as “a principal of Serotonin” with “an ownership interest in the entity”. Co-founder Matthew Iles, listed from 2021 to 2023, no longer appears on the site, and no other shareholder is named anywhere public.

Which clients can be confirmed?

Bit Digital, through its own SEC filings, with scope, price and dates. Sotheby’s, through Decrypt’s 2021 reporting that the Sotheby’s Metaverse ran on Mojito, the platform Serotonin built and spun out. CMT Digital, on the clients page, also led the seed round of Serotonin’s second spinout, Franklin. The remaining names on the 73-strong list carry no dates, scopes or results.

Does Serotonin have Clutch or Trustpilot reviews?

No. On 3 November 2026 Trustpilot had no profile for serotonin.co and Clutch had no listing for this company. Its public record is press coverage of the Mojito and Franklin funding rounds, Cassatt’s Wiley book and the Bit Digital filings, none of which is a client reviewing the work.

What is Serotonin’s link to Bit Digital?

Bit Digital (Nasdaq: BTBT) hired Serotonin on 18 June 2025 at $30,000 a month, a week before announcing its shift to an Ethereum treasury strategy. On 9 December 2025 it elected Cassatt to its board from 1 January 2026, with $200,000 in restricted stock issued to a Hong Kong entity she controls, and it renominated her in June 2026. The retainer was still running in the quarterly report filed in August 2026, and every filing discloses it as a related-party transaction.

Is Serotonin a good fit for a crypto ad campaign?

No. It sells narrative, social, earned media, research, recruiting and compliance on a retainer, not placements or paid reach. For a release, the wires in our PR distribution comparison start at $1,399; for traffic, the networks in our crypto ad networks ranking start at $100. Serotonin is for the brief those tools cannot carry: a thesis, a founder’s voice and the press that follows it.

Sources

The figures above come from these pages, published by the companies themselves unless noted. "Checked" is the date we last read each page.

1. Serotonin homepage ("go-to-market platform for web3, AI, and biotech", nav links) checked 3 Nov 2026
2. Marketing page ("Full Service Web3 Marketing Agency") checked 3 Nov 2026
3. Strategy page checked 3 Nov 2026
4. Research page (Serotonin Research) checked 3 Nov 2026
5. Recruiting page checked 3 Nov 2026
6. Business & Compliance Services page checked 3 Nov 2026
7. Products page (Spindl, Mojito, Franklin) checked 3 Nov 2026
8. Clients page (73 names) checked 3 Nov 2026
9. Team page (42 cards) checked 3 Nov 2026
10. se.ro Terms of Service, last revised 8 May 2025 (Serotonin Inc. + Serotonin Holdings LLC, non-refundable memberships, arbitration) checked 3 Nov 2026
11. se.ro Privacy & Cookies Policy, 8 May 2025 checked 3 Nov 2026
12. Serotonin Services Intake form (free-text monthly budget question) checked 3 Nov 2026
13. se.ro platform homepage checked 3 Nov 2026
14. Lever job board (2 postings) checked 3 Nov 2026
15. Homepage as archived 19 Feb 2021 ("marketing firm and product studio", co-founders Cassatt and Iles) checked 3 Nov 2026
16. Homepage as archived 26 Feb 2024 ("leading web3 marketing and product studio") checked 3 Nov 2026
17. Team page as archived 24 Feb 2024 checked 3 Nov 2026
18. Marketing services page as archived 2 Apr 2023 (eight service lines) checked 3 Nov 2026
19. Consulting Agreement dated 18 June 2025 between Bit Digital Inc. and Serotonin Inc. (Exhibit 10.02: $30,000 monthly retainer, payment terms, New York law) checked 3 Nov 2026
20. Bit Digital 8-K of 12 December 2025 (Cassatt elected to the board, $200,000 RSUs, consulting agreement summary) checked 3 Nov 2026
21. Director Agreement dated 10 December 2025 between Bit Digital Inc. and Amanda Cassatt checked 3 Nov 2026
22. Bit Digital DEF 14A of 8 June 2026 (director compensation: $207,143 consulting fees for 2025; re-nomination) checked 3 Nov 2026
23. Bit Digital 10-K for 2025 (related-party note on the Serotonin agreement) checked 3 Nov 2026
24. Bit Digital 10-Q for the quarter ended 30 June 2026 ("The Company pays Serotonin a monthly cash retainer of $30,000") checked 3 Nov 2026
25. Bit Digital press release of 25 June 2025 announcing the Ethereum treasury strategy checked 3 Nov 2026
26. Decrypt, 21 Oct 2021: Mojito spins out of Serotonin with $20 million at a $100 million valuation checked 3 Nov 2026
27. Decrypt, 4 Apr 2023: Franklin raises $2.9 million, second Serotonin spinout checked 3 Nov 2026
28. Mojito partners page (Serotonin listed as an agency partner) checked 3 Nov 2026
29. Franklin homepage (testimonial from Serotonin's Director of Finance) checked 3 Nov 2026
30. Spindl homepage (Serotonin in the customer strip; "Spindl is joining Coinbase") checked 3 Nov 2026
31. Wiley: Web3 Marketing by Amanda Cassatt, April 2023 checked 3 Nov 2026
32. Built In Chicago company profile (Year Founded: 2020, remote) checked 3 Nov 2026
33. Trustpilot (no profile) checked 3 Nov 2026
34. Clutch search (no profile for Serotonin Inc.) checked 3 Nov 2026

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