A hard fork that activated on the Stacks network in late October 2024 anchors every Stacks transaction to Bitcoin's own settlement layer, so reversing one now requires rewriting Bitcoin itself. The upgrade underpins sBTC and Bitcoin-backed staking products built on the network's Proof-of-Transfer consensus.
Reversing a confirmed transaction on the Stacks network now requires rewriting Bitcoin's own blockchain. That is the result of the Nakamoto upgrade, a hard fork that activated on Stacks in late October 2024 around Bitcoin block 867,867. The change ties every Stacks transaction directly to Bitcoin's settlement layer instead of loosely coupling the two chains.
How the upgrade rewires block production
Before Nakamoto, Stacks processed transactions on its own block cadence, connected to Bitcoin but not bound to it at the state level. Now, Stacks miners commit to a block at Bitcoin block N, and the state from that block gets written to Bitcoin at block N+1. Once the next Bitcoin block arrives, every Stacks miner must build on that same chain tip, closing off any fork path that bypasses Bitcoin's ledger.
Stacks runs on a Proof-of-Transfer consensus model, where miners bid Bitcoin to earn the right to produce Stacks blocks. The Nakamoto upgrade extended that connection to the ledger level, so security and state settlement are now both rooted in Bitcoin's chain. Smart contracts on the network are written in Clarity, a decidable language that does not compile to bytecode, meaning contract behavior can be fully analyzed before execution.
sBTC inherits the same settlement guarantee
sBTC, a Bitcoin-backed asset that launched on Stacks' mainnet in December 2024, was one of the first major products built on top of the upgrade. It lets Bitcoin holders move value into Stacks-based applications, including DeFi protocols and yield products, without wrapping through a centralized custodian.
That guarantee closes a specific attack surface. With weaker finality models, an adversary could in theory reverse a transaction after a user already received funds on the other side of a bridge; on post-Nakamoto Stacks, the attacker would also have to reorg Bitcoin itself. Bitcoin staking products sit under the same umbrella, letting users lock STX and earn Bitcoin yield through the Proof-of-Transfer mechanism.
A finality claim without caveats
Other approaches to programmability near Bitcoin rely on sidechains with federated bridges, rollups that post state roots to Bitcoin but require sequencer trust in the interim, or payment channel networks built for narrower use cases. Stacks' post-Nakamoto position carries no "assuming the bridge operators are honest" caveat and no challenge-period asterisk, since the settlement guarantee comes directly from Bitcoin's own block production.
Block times on Stacks stay tied to Bitcoin's roughly ten-minute cadence for tenure boundaries, though block production within a tenure runs faster than it did before the upgrade. STX, the network's native token for fees and staking, sits at the center of that model: demand for block space feeds directly into demand for the token.
Source: Crypto Briefing
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