Stacks has tightened its connection to Bitcoin following the Nakamoto upgrade, making the settlement of confirmed transactions dependent on the Bitcoin chain itself. The upgrade, activated in late October 2024 around Bitcoin block 867,867, means that reversing a finalized Stacks transaction would require reorganizing Bitcoin.
Before Nakamoto, Stacks produced blocks on its own cadence while maintaining a broader connection to Bitcoin. The upgrade changed that structure by tying each Stacks block tenure directly to a Bitcoin block. Stacks miners commit to a block at Bitcoin block N, while the resulting state is recorded on Bitcoin at block N+1. Once that next Bitcoin block is confirmed, miners must continue building on the same chain tip.
How Stacks’ Bitcoin settlement works
This design removes a separate fork path that could bypass Bitcoin’s ledger. Stacks therefore describes the result as 100% Bitcoin finality: the network’s transaction settlement is anchored to the same chain that provides Bitcoin’s own irreversibility, rather than relying only on an independent confirmation process or a separate challenge period.
Stacks uses Proof of Transfer, a consensus model in which miners commit Bitcoin to compete for the opportunity to produce Stacks blocks. Nakamoto extended that Bitcoin connection from the consensus mechanism to the settlement layer. Stacks smart contracts are written in Clarity, a decidable language designed so contract behavior can be analyzed before execution.
sBTC brings Bitcoin liquidity to Stacks applications
The upgrade became a foundation for applications such as sBTC, a Bitcoin-backed asset that launched on mainnet in December 2024. sBTC is designed to let Bitcoin holders use value on Stacks-based applications, including decentralized finance and yield products, without relying on a centralized custodian or a conventional bridge with separate trust assumptions.
Bitcoin-linked finality is particularly relevant for assets moving between networks. If a transaction on a weaker settlement system were later reversed after funds had arrived on the other side of a bridge, users could face a significant loss. Under Stacks’ post-Nakamoto model, an equivalent reversal would require an attacker to reorganize Bitcoin as well, substantially increasing the economic cost of the attack.
The same settlement framework also applies to Bitcoin staking products in the Stacks ecosystem. Users can lock STX and seek Bitcoin-denominated yield through the Proof of Transfer mechanism, while the related staking records receive the same finality as other confirmed Stacks transactions.
Stacks’ position among Bitcoin scaling systems
Projects seeking to add programmability to Bitcoin use several different approaches, including federated or threshold-multisignature sidechains, rollups that post state data to Bitcoin and payment-channel networks. Some designs still depend on bridge operators or sequencers, while others are optimized for specific transaction types.
Stacks’ distinguishing claim after Nakamoto is that its settlement is directly tied to Bitcoin block production rather than being conditional on the continued honesty of bridge operators or the expiration of a challenge window. Stacks tenure boundaries follow Bitcoin’s roughly 10-minute block cadence, although transactions within a tenure can be produced more quickly than before the upgrade.
STX remains central to the network’s economic model, serving as the native token for transaction fees and staking. As applications and demand for block space grow, activity on Stacks can translate into additional demand for STX.
