Ostium is on a simple mission: make it possible for anyone with a digital wallet to trade stocks, commodities, currencies, and crypto with full transparency. No brokers, no freezes, no hidden spreads. We’re replacing the opaque, offshore brokerage model with a transparent, permissionless trading stack built onchain. Every trade, deposit, and withdrawal is verifiable through open, auditable code. We’ve raised $27.9M+ from General Catalyst, Jump, LocalGlobe, Susquehanna (SIG), GSR, Alliance DAO, Soma Capital, Balaji Srinivasan, Meltem Demirors, and others.

Role

Remote / Full-Time

About Ostium

Ostium is building the neo-broker for the onchain world, one place to trade the world's markets, with the depth and execution of an institutional desk and the openness of a public blockchain.

Global markets still run on infrastructure built decades ago: opaque brokers, black-box pricing, permissioned and geography-gated access. Meanwhile, a new kind of trader, global, self-directed, cross-asset, stablecoin-native, has outgrown all of it.

That trader is who we're building for. Real-world assets are moving onchain fast, and there's more than one way to get there. Much of the industry is working to rebuild that liquidity onchain from the ground up. We took a different view: the world's deepest markets, the venues that price global oil, gold, currencies, and equities, already hold the liquidity traders want. What's broken is access to it. So we built the genuinely hard part: the legal, operational, and technical infrastructure to connect directly into those markets and route their liquidity onchain, to anyone with a wallet. Prime-broker-grade access, in the hands of the individual trader, with every spread, liquidation, and dollar of collateral verifiable onchain.

And it's working. Traders now run eight-figure positions through Ostium, including the largest onchain oil trade ever executed, because nothing else onchain can hold that size. We're defining a new category, and we're already ahead in it.

Why Now

Perpetuals just went mainstream. US regulators have opened the door to digital commodity perps, the products are in every major outlet, and real-world assets are moving onchain faster than anyone predicted. The winds have never been more at our back. The demand we built for is arriving in force, and the window to define this category is open now.

Traction

We've raised $27.9M+ from General Catalyst, Jump, Susquehanna (SIG), Wintermute, and angels including Balaji Srinivasan and Meltem Demirors. Our highest-retention traders are whales who stay on product merit alone, not because of incentives, often requesting size in a way that verges on OTC. Record block trades run through us because the liquidity model is built for exactly that.

How We Work

We're a 30-person team across New York, Miami, and Porto, Portugal, and every time zone in between. Our founding team includes Harvard and Bridgewater alumni, along with medalists in International Olympiads (Physics, Biology).

We're here to win, which means shipping fast and staying obsessed with what our traders actually need. We're a meritocracy, not a democracy. We debate hard, but once a call is made we disagree and commit, then row together. We also believe being AI-native is one of the only ways to scale properly. Our best operators and engineers know how to leverage AI without ever surrendering their judgment to it. Lead and hone your own intuition, but leverage the machine to scale your efforts.

We know the cost of the old way firsthand. We started Ostium in a hacker house at Harvard after an offshore broker froze our accounts and kept our deposits. If you can't verify it, you don't own it. That conviction is now infrastructure.

Building the neo-broker layer takes range: markets, pricing, risk, engineering, design, and operations. If that's you, there's no second best.

Role Overview

As Ostium's Controller, you will direct our accounting operations and implement institutional-grade financial frameworks. Your mandate is to establish and oversee robust systems for our month-end close, internal control environment, onchain reconciliation infrastructure, and comprehensive audit readiness. You will sit across two accounting worlds that almost no one has had to reconcile simultaneously: institutional-grade NAV and positions accounting on the TradFi side, and onchain protocol accounting, stablecoin collateral, token flows, and fee, spread, and liquidation revenue, on the DeFi side. Your mandate is to make our fiat books as rigorous and verifiable as the blockchain itself.

We are backed by Tier 1 institutions like Jump, SIG, General Catalyst, and Wintermute, and institutional traders already run eight-figure positions through our protocol. This means our financials must be bulletproof, auditable, defensible, and closed on a cadence that a serious board and top-tier auditors expect.

Core Responsibilities

• Consolidated Close: Own the monthly and quarterly close across all entities, consolidating fiat and onchain activity into clean US GAAP financials on a predictable cadence.

• NAV & Positions Accounting: Value the protocol's collateral pool, open positions, and P&L. Account for and reconcile fee, funding, spread, and liquidation revenue. Reconcile onchain state to the books daily, not monthly.

• Digital Asset Accounting: Own crypto treasury, stablecoin flows, wallet-level reconciliation, gas, and protocol revenue, while applying digital asset fair value treatment correctly.

• Controls & Reconciliation Infrastructure: Build the reconciliation and control environment from the ground up, wiring onchain data directly into the books. This is an AI-native function. You'll leverage tooling to reconcile at chain speed rather than throwing headcount at the problem.

• Audit & Tax: Manage external auditors and drive first audit readiness. Coordinate crypto and multi-entity tax across jurisdictions. Support entity structuring.

• Treasury & Reporting: Manage cash and stablecoin balances, runway, and collateral movements alongside trading and operations. Deliver investor and board reporting.

• Corporate Accounting Core: Own AP, payroll, vendor management, and equity/token compensation accounting.

Requirements

• CPA (Active): Deep US GAAP fluency and demonstrated ownership of a full audit-ready close.

• Dual-Domain Fluency: Real, hands-on experience in both TradFi (positions, NAV, brokerage, or fund accounting) and crypto/digital asset accounting. You can reconcile a margin book and a Web3 wallet in the same afternoon. This is the non-negotiable spine of the role.

• Relevant Environment: Experience at a broker-dealer, prime broker, hedge fund, fund administrator, or trading firm where you accounted for positions, margin, and mark-to-market, plus hands-on crypto-native accounting (onchain reconciliation, DeFi protocol revenue, stablecoins).

• Onchain Fluency: You can read a block explorer, deeply understand wallets and smart contract interactions, and reconcile directly against onchain data as your absolute source of truth.

• Systems: Fluency with a core ERP (QuickBooks) and a crypto subledger is important.

• High Agency: You've built or materially rebuilt a finance function in a fast-moving, resource-constrained environment. You escalate with proposed fixes, not just variances, and you're perfectly comfortable being the entire function before you build a team.

• Bonus: Multi-entity international experience, VC-backed startup audit and fundraising support, and deep expertise in crypto tax.

Why Ostium?

We are small, elite, and we work hard, not for optics, but because we care deeply about what we are building. You will receive a highly competitive compensation package, flexible work arrangements, and the opportunity to work alongside a team that cares deeply about the craft, while owning the product at the center of a new category.