# What is xstrkBTC?

#### xstrkBTC: Liquid staking for shielded Bitcoin

> xstrkBTC is the liquid staking token issued by Endur for staked strkBTC, Starknet's shielded Bitcoin asset. It is the fifth BTC LST on Endur and the first that carries optional privacy properties through to the staked position.

***

#### **What is strkBTC?**

[strkBTC](https://www.starknet.io/blog/strkbtc-starknets-shielded-bitcoin-with-private-transactions/) is Starknet's native shielded Bitcoin. Each unit is 1:1 backed by BTC, redeemable for native BTC, and issued deterministically against verified deposits to a multi-institution federation multisig. Issuance was ratified by [SNIP-38](https://community.starknet.io/t/snip-38-strkbtc-bitcoin-on-starknet/116174) and SNIP-39.

strkBTC operates in two modes:

| **Mode**       | **Behaviour**                                                                                   |
| -------------- | ----------------------------------------------------------------------------------------------- |
| **Unshielded** | Standard ERC-20. Public balances and public transfers.                                          |
| **Shielded**   | Private balances and transfers. Amounts and counterparties hidden via Starknet zk-STARK proofs. |

Mode is reversible. Holders move between shielded and unshielded contextually without bridging into a different token.

For background on strkBTC's underlying technology, see Starknet's [STRK20 standard](https://www.starknet.io/blog/make-all-erc-20-tokens-private-with-strk20/)

<figure><img src="/files/0WxuQK7FfI6k9qkPWer4" alt=""><figcaption></figcaption></figure>

***

#### **What is xstrkBTC?**

xstrkBTC is the LST that represents staked strkBTC on Endur. Like the rest of Endur's BTC LST stack, it is yield-bearing through exchange rate appreciation. Unlike the rest, xstrkBTC inherits the privacy properties of its underlying.

**Key properties:**

* 1:1 to staked strkBTC at issuance, exchange rate rises with rewards
* Yield is paid in strkBTC (the same asset deposited)
* Composable across Starknet DeFi: lending, LPs, vaults
* Inherits the shielded or unshielded mode of the underlying strkBTC
* Withdrawals tracked by NFT, with deposit-withdrawal matching for faster exits

***

#### **How yield works**

1. Starknet's protocol allocates a portion of total STRK emissions to BTC stakers.
2. Endur receives those STRK rewards on behalf of the strkBTC delegated through its validator registry.
3. A swap extension converts STRK into strkBTC at protocol-routed venues.
4. The strkBTC accrues into the vault, raising the xstrkBTC ↔ strkBTC exchange rate.

The xstrkBTC token balance does not change. The amount of strkBTC redeemable per xstrkBTC increases over time.

There is no rebasing, no airdrop dependency, and no off-chain reward distribution.

***

#### **Privacy: what is public, what is private**

| **State**                                                   | **Visibility** |
| ----------------------------------------------------------- | -------------- |
| xstrkBTC ↔ strkBTC exchange rate                            | Public         |
| Total supply of xstrkBTC                                    | Public         |
| Validator set and reward flows                              | Public         |
| Aggregate vault state                                       | Public         |
| Individual strkBTC and xstrkBTC balances (in shielded mode) | Private        |
| Transfer amounts and counterparties (in shielded mode)      | Private        |

Privacy applies to user state, not to protocol state. Solvency and yield accounting remain auditable. For compliance use cases, viewing keys allow selective disclosure of strkBTC activity through a threshold-controlled auditing entity.

***

#### **Fees**

| **Item**        | **Detail**                               |
| --------------- | ---------------------------------------- |
| Stake fee       | 0                                        |
| Redemption fee  | 0                                        |
| Performance fee | 15% on earned rewards only               |
| Yield mechanism | Exchange rate appreciation, not rebasing |

The performance fee applies to rewards, not to principal. Entering and exiting xstrkBTC is free.


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