Horizon Exchanges

Horizon’s exchange model: prediction markets, crypto, stocks, and multi-exchange support.

Horizon supports ten exchange backends that all implement the same Exchange trait. You can trade on a single exchange or multiple exchanges simultaneously.

Prediction Markets

Paper

Local simulated exchange with tick-based matching. No credentials needed. Default for development.

Polymarket

Largest prediction market on Polygon. EIP-712 signed orders via the CLOB API.

Kalshi

US-regulated (CFTC) prediction market. REST API with bearer token auth.

Limitless

Base chain prediction market. REST client for on-chain trading.

Traditional & Crypto

Alpaca

Commission-free stock and ETF trading. Paper and live modes.

Coinbase

Crypto exchange with deep liquidity. HMAC-SHA256 auth via Advanced Trade API.

Robinhood

Commission-free crypto trading via REST API.

Hyperliquid

Decentralized perpetuals + spot on its own L1 chain. Wallet-based EIP-712 auth.

Interactive Brokers

Multi-asset broker: stocks, options, futures, and ForecastEx prediction markets. Bridges equities/options and prediction market trading.

Exchange Model

All exchanges implement a common trait:

trait Exchange {
    fn submit_order(&self, request: &OrderRequest) -> Result<String>;
    fn cancel_order(&self, order_id: &str) -> Result<()>;
    fn cancel_all(&self) -> Result<usize>;
    fn cancel_for_market(&self, market_id: &str) -> Result<usize>;
    fn drain_fills(&self) -> Vec<Fill>;
    fn fetch_positions(&self) -> Result<Vec<Position>>;
}

The Engine wraps exchanges in an ExchangeBackend enum for dispatch without trait objects:

ExchangeBackend::Paper(PaperExchange)
ExchangeBackend::Polymarket(PolymarketExchange)
ExchangeBackend::Kalshi(KalshiExchange)
ExchangeBackend::Alpaca(AlpacaExchange)
ExchangeBackend::Coinbase(CoinbaseExchange)
ExchangeBackend::Hyperliquid(HyperliquidExchange)
ExchangeBackend::Robinhood(RobinhoodExchange)
ExchangeBackend::IBKR(IBKRExchange)

Single vs Multi-Exchange

Single exchange (default)

# Paper (implicit)
hz.run(name="simple", markets=["test"], pipeline=[...])

# Single live exchange
hz.run(
    name="poly_mm",
    exchange=hz.Polymarket(private_key="0x..."),
    mode="live",
    ...
)

Multi-exchange

hz.run(
    name="cross_venue",
    exchanges=[
        hz.Polymarket(private_key="0x..."),
        hz.InteractiveBrokers(paper=True),
        hz.Coinbase(),
    ],
    mode="live",
    ...
)

See Multi-Exchange for details on routing, netting, and cross-venue strategies.

Fill Model

All exchanges use a pull model for fills:

Exchange	Fill Source	Method
Paper	tick(market_id, mid_price)	Matches orders against mid price
Polymarket	drain_fills() → poll_fills_async()	Polls /trades endpoint
Kalshi	drain_fills() → poll_fills_async()	Polls /portfolio/fills endpoint
Alpaca	drain_fills() → poll_fills_async()	Polls /v2/orders?status=filled
Coinbase	drain_fills() → poll_fills_async()	Polls /orders/historical/fills
Robinhood	drain_fills() → poll_fills_async()	Polls /crypto/trading/orders/?status=filled
IBKR	drain_fills() → poll_fills_async()	Polls /iserver/account/trades
Hyperliquid	drain_fills() → poll_fills_async()	Polls /info with userFillsByTime

The strategy loop calls poll_fills() each cycle for live exchanges, and tick() for paper exchanges.

Order Routing

When you submit an order via hz.run(), it’s automatically routed to the correct exchange based on the market.exchange field:

• Markets resolved as "polymarket" → routed to the Polymarket backend
• Markets resolved as "kalshi" → routed to the Kalshi backend
• Markets with "alpaca" → routed to the Alpaca backend
• Markets with "ibkr" → routed to the IBKR backend
• Markets with "coinbase" → routed to the Coinbase backend
• Markets with "robinhood" → routed to the Robinhood backend
• Markets with "hyperliquid" → routed to the Hyperliquid backend
• Markets with "paper" or empty exchange → routed to the primary exchange

You can also explicitly specify the exchange when using the Engine directly:

engine.submit_order(request, exchange="polymarket")
engine.submit_quotes("market_id", quotes, Side.Yes, exchange="kalshi")

Side Mapping

Exchange	Side Used	Notes
Polymarket	Side.Yes / Side.No	Binary prediction contracts
Kalshi	Side.Yes / Side.No	Binary prediction contracts
Limitless	Side.Yes / Side.No	Binary prediction contracts
Alpaca	Side.Long	Equities — no Yes/No concept
Coinbase	Side.Long	Crypto — no Yes/No concept
Hyperliquid	Side.Long	Perps/spot — no Yes/No concept
Robinhood	Side.Long	Crypto — no Yes/No concept
IBKR	Side.Long	Multi-asset — no Yes/No concept
Paper	Any	Copies the side from the order request

Exchange Fields on Types

Orders, Fills, and Positions all carry an exchange field indicating which exchange they belong to:

order.exchange      # "polymarket", "kalshi", "alpaca", "coinbase", "hyperliquid", "robinhood", "ibkr", or "paper"
fill.exchange       # "polymarket", "kalshi", "alpaca", "coinbase", "hyperliquid", "robinhood", "ibkr", or "paper"
position.exchange   # "polymarket", "kalshi", "alpaca", "coinbase", "hyperliquid", "robinhood", "ibkr", or "paper"