A coffee roaster in Austin runs a Shopify storefront, books revenue in QuickBooks, and settles card payments through Stripe. Castle, a Miami-based fintech, wants a slice of that daily flow routed into bitcoin before the owner ever logs in.
The company markets itself as an automated bitcoin treasury solution for small and medium businesses [Castle]. The wedge is plumbing. Castle integrates with PayPal, Shopify, and Stripe to sweep a configurable percentage of sales proceeds into bitcoin, with bookkeeping reconciled through QuickBooks and Square [Nasdaq] [Castle Website]. Owners pick a percentage. The platform handles the conversion and the ledger entry.
In June, the company said it raised roughly $1 million in seed funding led by Boost VC, with participation from Winklevoss Capital, Park Rangers Capital, Epoch VC, and angels [Fintech Review]. Bitcoin Magazine and Yahoo Finance carried the same figure [Bitcoin Magazine] [Yahoo Finance]. The proceeds are earmarked for platform development and onboarding U.S. SMBs [Financial News].
The bet
Castle is building for a customer that public-company treasury vendors largely ignore. MicroStrategy popularized the corporate bitcoin treasury thesis at billion-dollar scale. The named retail-facing competitors, Swan Bitcoin and River Financial, have historically catered to individual savers and high-net-worth accounts. Castle's pitch is that the same logic, dollar-cost averaging into bitcoin out of operating cash flow, should be available to a dentist's office, a Shopify merchant, or a regional services firm without a CFO or a custody desk.
The product choice that matters is the integration surface. By plugging directly into the systems where SMB revenue already lands (Stripe, Square, PayPal, Shopify) and the books where it gets recorded (QuickBooks), Castle is trying to make the conversion feel like a payroll deduction rather than a trading decision [Nasdaq]. That framing is the difference between a product an owner sets up once and one they have to think about every week.
Why it could be big
The investor list is the loudest signal in the file. Winklevoss Capital is one of the most established crypto-native funds in the United States, and Boost VC has been backing bitcoin infrastructure since 2014. Park Rangers Capital and Epoch VC round out a syndicate that is unambiguously aligned with the thesis [Fintech Review]. None of these names write checks into bitcoin treasury startups for storytelling purposes. They write them because they believe SMB adoption is the next leg of corporate bitcoin allocation after the public-company wave.
The macro setup is favorable to that view. The SEC's approval of spot bitcoin ETFs in 2024 normalized bitcoin as a balance-sheet asset for traditional finance. Accounting treatment has loosened, with FASB rules now permitting fair-value reporting of crypto holdings, removing one of the longstanding deterrents for owner-operators who did not want to book impairments on a volatile asset. If even a low-single-digit percentage of U.S. SMBs decided to sweep one or two percent of revenue into bitcoin, the addressable flow would be significant. Castle is positioned to be the rails for that behavior.
The team and the round
Castle was co-founded by João Almeida and Stephen Cole [Refresh Miami]. Almeida is listed as CTO and co-founder on his LinkedIn profile [LinkedIn]. The company is headquartered in Miami, a city that has aggressively courted crypto-native fintechs since 2021 and now hosts a dense cluster of bitcoin-focused builders and capital.
The round itself is small by 2025 fintech standards but appropriate for the stage and the wedge. Castle is not trying to win on capital intensity. It is trying to win on integrations, trust, and the unglamorous work of making a regulated conversion flow function inside the accounting stack a small business already uses.
| Round | Date | Amount | Lead |
|---|---|---|---|
| Seed | June 27, 2025 | $1.0M | Boost VC |
Participating investors: Winklevoss Capital, Park Rangers Capital, Epoch VC, and angels [Fintech Review].
What the bears say
The most credible pushback is regulatory. Routing customer revenue into bitcoin on behalf of a business touches money transmission, custody, and tax reporting, three areas where the U.S. rulebook is still being written round by round. Swan Bitcoin and River Financial have spent years building licensing footprints and compliance teams to operate in this space, and a $1 million seed does not buy a fifty-state money transmitter license. Castle's most plausible answer, supported by the integration list, is that it is positioning as a software layer on top of regulated payment processors and exchange partners rather than as the principal in the conversion. That model has worked for other fintechs that orchestrate flows without holding the regulatory burden directly. Whether it holds up as Castle scales onboarding nationally is the open question [Fintech Review].
There is also a category question. If Stripe, Square, or QuickBooks decided to ship native bitcoin treasury features, Castle would face a distribution problem overnight. The counterargument is that incumbents have shown limited appetite to take on crypto custody risk on their own balance sheets, which is precisely why a focused third party can win the wedge.
What to watch
Three things over the next twelve months. First, customer disclosures. Castle has not yet released public numbers on merchants onboarded or assets converted, and the first credible traction figure will reset how investors price the next round. Second, the licensing posture. Watch whether Castle files for state money transmitter licenses directly or stays purely in the software-orchestration lane. Third, a Series A. A $1 million seed from this caliber of syndicate is typically a bridge to a larger round within twelve to eighteen months, and the lead on that round will tell you whether generalist fintech investors are ready to underwrite SMB bitcoin treasury as a category or whether it remains a crypto-native thesis.