Cassie finds the trade on X. Definitive powers the execution.

“We built on Definitive because managing trading infrastructure across venues was taking time away from what makes Cassie special: finding opportunities. Flash API gives us the best execution, so users only need to think about the opportunity.”

Celestine, Founder of Cassie

Highlights

• Cassie is an “opportunity terminal” that turns what traders post on X into real trades they can act on in minutes.
• Every spot order runs on Definitive’s Flash API, from entry through staged take profits, stop losses, and exit.
• 30 minutes to live. Cassie’s own AI agent wrote the Flash integration and had it running in half an hour.
• One API replaced a stack of venues. Cassie no longer maintains per-venue infrastructure or liquidity to support the assets its users want.
• Open source. Cassie’s terminal code is public, making its Flash integration a working reference for any builder turning signals into trades.
• Engineering pointed at the edge. The team’s time now goes into AI-powered filters and opportunity ranking, not order plumbing.

What is Cassie?

Cassie is an “opportunity terminal” for crypto traders. It watches the conversation on X, where most trade ideas start, and turns market posts into opportunities with a clear plan attached: the thesis, the entry, the target, and the stop.

The problem Cassie solves is the gap between spotting a trade and taking it. A trader sees a call, opens another app, finds the token, checks the chain, sets up the order, and then has to babysit the position. By the time all of that is done, the opportunity has often moved.

Cassie’s bet is that discovery and execution belong in one experience. The trader finds the idea, reviews the plan, and approves it. Cassie handles the rest.

The challenge: building trading infrastructure across multiple chains

Surfacing good opportunities is the part of Cassie users see. Executing them well is the part that kept the team up at night.

In an earlier version of Cassie, the team ran its own infrastructure across several trading venues to support specific assets and chains. Each venue needed its own integration. Every new asset meant more plumbing to build and some required liquidity parked in anticipation of user trading activity.

And entry was only the start. Cassie’s promise is to manage a position all the way to exit. That means the full order lifecycle across chains: placing the trade, taking profits in stages, holding a stop loss, and moving protection as the trade develops. Building that in-house means owning conditional order monitoring, real-time pricing, routing, gas, nonces, slippage, retries, and MEV protection on every chain.

Every hour spent there was an hour not spent on the thing that makes Cassie worth using: finding the right opportunities. The team needed a dedicated execution partner so it could stop running venues and get back to building the product.

The solution: Definitive’s Flash API as Cassie’s execution rail

Definitive is an onchain trading platform for pro traders and institutions, built by Coinbase Prime and Tagomi alumni. Flash API exposes the same execution engine that professional desks use on Definitive’s terminal, and it now powers every spot trade Cassie places.

One integration in place of a stack of venues

Flash aggregates 900+ DEXs and onchain liquidity sources across 15+ chains on EVM and Solana. Cassie doesn’t connect to liquidity sources one by one or keep inventory on each. It sends an order, and Flash finds the most competitive route at the moment of execution, simulates the trade before execution, and reroutes when liquidity shifts.

The result is better fills on the opportunities Cassie surfaces, with none of the venue maintenance. As Definitive adds chains and venues, Cassie’s users get them automatically.

Full position management, from entry to exit

In Cassie, a user discovers an opportunity, reviews the trading plan, and approves it. From there Cassie manages the position on its own. Flash powers each step underneath:

• Market orders to enter the moment the user approves.
• Take Profit orders to scale out in stages as targets hit.
• Stop Loss orders to cap the downside from the start.
• Order updates and cancels so Cassie can tighten protection as the trade moves in the user’s favor.

Each order type is one parameter away from the others on the same API. Flash watches market conditions, executes when specific triggers are met, and handles gas, nonces, slippage, and MEV protection along the way. Users act on an opportunity without managing every step by hand.

Non-custodial execution for conditional orders

Flash is non-custodial by design, including for Limit, Stop Loss and Take Profit. Users approve once and sign each order offchain. Funds stay in the user’s wallet until an order is executed, then Flash swaps and settles back in a single atomic transaction. Open orders are held offchain, out of sight of MEV bots.

Built for agents, integrated by one

Flash is stateless, REST-based, and ships with LLM-optimized docs. That design paid off directly for Cassie. Celestine had Cassie’s AI agent do the integration, and it was up and running in 30 minutes. In Celestine’s words, it was “pretty much the easiest thing in the world.”

Engineering time routed to the opportunity layer

With execution handled, Cassie’s team is putting its time where the product wins: improving its AI-powered filters, refining how opportunities are identified and ranked, and making each one easier to evaluate and act on. That’s the part users can feel, and the part no execution API can build for them.

Real impact so far

Cassie’s biggest gains are in speed and focus, and because its terminal is open source, the proof is public.

• 30 minutes from first line of code to live execution, written by an AI agent.
• Zero venues to maintain. One API replaced Cassie’s per-venue infrastructure.
• Better execution quality on the opportunities Cassie surfaces, through Flash’s smart routing.
• A public reference build. Any developer can read Cassie’s open-source code and see exactly how an opportunity becomes a managed trade on Flash.

What’s Next

Cassie’s roadmap is about sharper discovery: better filters, better ranking, and opportunities that are easier to trust and act on. Every one of those improvements lands on the same execution rail, with no new venues to wire up.

Definitive’s mission is to bring professional-grade execution to everyone. Flash API is how that reaches beyond Definitive’s own terminal and mobile app. Wallets, apps, and AI agents can plug into the same smart router, the same advanced order types, and the same multi-chain coverage that institutional desks rely on, through one API.

Cassie shows what that looks like in practice. A small team, an AI agent, and 30 minutes turned an opportunity feed into a full trading product.

Learn more about Cassie: cassie.trade | X: @cassiedottrade | Cassie’s open source repo

Learn more about Definitive’s Flash API: flash.definitive.fi/docs | X: @definitivefi