> For the complete documentation index, see [llms.txt](https://docs.leather.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.leather.io/learn/proof-of-transfer-pox.md).

# What Is Proof-of-Transfer (PoX)?

Proof of Transfer (PoX) is Stacks' consensus mechanism. Miners spend BTC to produce Stacks blocks, and that BTC rewards STX stakers.

Proof of Transfer (PoX) is how the Stacks blockchain picks who produces its blocks. Instead of burning energy (proof of work) or locking the chain's own token alone (proof of stake), Stacks miners spend BTC, which already carries Bitcoin's proof of work. That BTC goes to the people who stake STX.

## How it works

* **Miners** send BTC in a Bitcoin transaction to bid for the right to produce Stacks blocks. A weighted random draw picks the winner; a larger bid has a better chance. The winner earns new STX and transaction fees.
* **Stakers** lock STX with a pool for one or more reward cycles. A reward cycle is 2,100 Bitcoin blocks, about two weeks.
* **Signers**, chosen through staked STX, approve each Stacks block. A block needs approval from signers holding 70 percent of the signing weight.

Each group of Stacks blocks is tied to a Bitcoin block. Rewriting Stacks history would mean rewriting Bitcoin history as well.

## PoX-5

PoX-5 activated at Bitcoin block 960,230 on July 30, 2026. Since then, the BTC miners spend goes to an sBTC deposit address controlled by the protocol. The protocol pays it out as sBTC rewards to STX-only stakers and, through protocol bonds, to Bitcoin Staking participants. Before PoX-5, miners paid BTC directly to stakers' reward addresses.

## Trade-offs

* PoX reuses Bitcoin's existing proof of work instead of adding its own.
* Stacks depends on Bitcoin: a problem on Bitcoin affects Stacks.
* Mining power can concentrate among a few miners.

See [What Makes Staking on Stacks Different?](/learn/what-makes-stacking-on-stacks-different-from-staking.md) and [Getting started with STX-only staking](/stacking/getting-started-with-stacking.md).