> For the complete documentation index, see [llms.txt](https://docs.txflow.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.txflow.com/perp/contract-specifications.md).

# Contract Specifications

### What Are Perpetuals?

TxFlow perpetuals are derivative products with **no expiration date**. They maintain price convergence with the underlying spot asset through **funding payments** rather than settlement dates. For details on the funding mechanism, see [Funding](/perp/funding.md).

### Contract Specifications

TxFlow maintains a streamlined specification model with **minimal contract-specific restrictions** and **no address-level limitations**.

<table data-header-hidden><thead><tr><th width="238.375">Parameter</th><th>Specification</th></tr></thead><tbody><tr><td>Instrument Type</td><td>Linear perpetual</td></tr><tr><td>Contract Size</td><td>1 unit of underlying spot asset</td></tr><tr><td>Underlying Asset</td><td>TxFlow oracle index of spot asset</td></tr><tr><td>Initial Margin Fraction</td><td>1 / (user-selected leverage)</td></tr><tr><td>Mark Price</td><td>See <a href="/pages/lWdZgI2P4YIODQ7uazsl">Mark Price and Oracle Price</a></td></tr><tr><td>Delivery / Expiration</td><td>N/A (hourly funding payments)</td></tr><tr><td>Account Type</td><td>Cross-margin or isolated margin (per wallet)</td></tr><tr><td>Position and Order Limit</td><td>See <a href="/pages/Whq0nZ2jGGayqyHTTFvA">Position and Order Limit</a></td></tr></tbody></table>