> ## Documentation Index
> Fetch the complete documentation index at: https://docs.hyperprop.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Execution and fills

> How orders fill against the HDL book on Hyperprop, and what to expect when you trade size.

Orders on HDL instruments fill against the HDL book. The book you see is the
book your orders execute against.

## Market orders

A market order takes liquidity from the best price outwards, as it would in a
real market. A small order fills at or near the best bid or ask. A large order
fills across several price levels, and your fill price is the average of those
levels. Size beyond the depth shown in the book is priced conservatively.

## Limit orders

A limit order fills when the market trades at your price. Larger limit orders
can fill in parts over time, as they would in the market, with the remainder
continuing to work.

## Live data only

Hyperprop fills orders only against current market data. If live data for an
instrument is interrupted, fills on that instrument pause until it resumes.

## What to expect at size

* **Small orders** pay the spread, which on HDL is among the tightest in the
  market.
* **Large orders** pay for the depth they consume. On deep markets such as BTC
  the cost is fractions of a basis point; on smaller assets it is larger.
* **Thinner markets** cost more to trade at size, just as they do in the
  market. Check the depth before sending a large market order, or use a limit
  order.

Because HDL brings depth together, a large order usually costs less on HDL than
in any single market, while still reflecting what the market would really
charge.

### Measured example

The cost of a \$1M market buy on 25 October 2026, in basis points from the mid
price.

| Asset | Deepest single market | HDL |
| - | - | - |
| BTC | 0.39 bp | 0.29 bp |
| SOL | 4.83 bp | 2.93 bp |
| XRP | 6.00 bp | 3.25 bp |

Execution costs change with market conditions. These figures are illustrative
and are not a guarantee of future fills.

> **Why was my fill worse than the top of book?**
>
> Your order was larger than the size shown at the best price, so it filled
> across several levels. The average of those levels is worse than the
> first one. This is how an order of that size fills in a real market.

> **Why did my limit order fill only partly?**
>
> Limit orders fill only for the volume that trades at your price. If less
> volume traded there than your order size, the rest keeps working.

> **What happens if a source goes down while I am trading?**
>
> HDL continues from its remaining sources, with a little less depth. If an
> instrument cannot be priced reliably, it pauses, and Hyperprop stops
> filling it until the book is back.


## Related topics

- [Transparency and audit](https://docs.hyperprop.com/hdl/transparency.md)
- [Get trade execution history](https://docs.hyperprop.com/trade-api/orders/get-trade-execution-history.md)
- [Real-time trading stream](https://docs.hyperprop.com/guides/realtime-trading-stream.md)
- [Changelog](https://docs.hyperprop.com/changelog.md)
- [Get fills for a trading day](https://docs.hyperprop.com/platform-api/reconciliation/get-fills-for-a-trading-day.md)


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