# Chain consensus (/docs/concepts/chain-consensus)

Subtensor currently uses **Proof of Authority (PoA)** for blockchain consensus.
A permissioned set of validator authorities produces and finalizes blocks. This
is separate from [Yuma Consensus](/docs/internals/consensus), which determines
how subnet participants are evaluated and rewarded.

## Current mechanism: Proof of Authority [#current-mechanism-proof-of-authority]

Subtensor separates block production from finality:

| Layer            | Current mechanism                             | Role                                                                                                                                                |
| ---------------- | --------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------- |
| Block production | [Aura](/code/runtime/src/lib.rs#L363-L369)    | Assigns block-production slots to members of the authorized validator set.                                                                          |
| Block finality   | [GRANDPA](/code/runtime/src/lib.rs#L371-L381) | Finalizes a chain after more than two-thirds of authority voting weight agrees, making its blocks irreversible under the protocol's finality rules. |

Only approved authorities can author blocks or vote on finality. Other nodes can
independently verify the chain, relay blocks and transactions, and expose RPC
services, but they do not join the authority set merely by running a node or
holding TAO.

The authority set can be changed through privileged on-chain administration.
This permissioned validator selection is why the current chain-level mechanism
is classified as PoA.

## Planned transition to Nominated Proof of Stake [#planned-transition-to-nominated-proof-of-stake]

The roadmap is to replace PoA with **Nominated Proof of Stake (NPoS)**. Under
NPoS, validator selection is stake-backed: nominators support validator
candidates, and the active validator set is selected from that support.

The current roadmap targets this transition within roughly the next year. This
is a planning estimate, not a fixed activation date. Implementation details and
timing may change before on-chain activation.

Until that transition is activated on-chain, Subtensor remains a PoA network.

## Chain consensus and Yuma Consensus [#chain-consensus-and-yuma-consensus]

The term “consensus” appears in two different contexts in Bittensor:

* **Chain consensus** decides who may produce blocks and when those blocks are
  final. It currently uses PoA with Aura and GRANDPA.
* **Yuma Consensus** aggregates subnet validators' miner evaluations and helps
  determine participant incentives. It does not produce or finalize blockchain
  blocks.

See [Yuma Consensus](/docs/internals/consensus) for the subnet-level mechanism.