> For the complete documentation index, see [llms.txt](https://polarischain-1.gitbook.io/polarischain/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://polarischain-1.gitbook.io/polarischain/8.-network-layer-and-protocol-operations/8.6-protocol-upgrades-and-rolling-choreography.md).

# 8.6 - Protocol Upgrades & Rolling Choreography

Polarischain implements an **epoch-bound, 2/3-signal-flip upgrade model** that enables continuous evolution without hard forks or chain splits.

**Upgrade Flow**

1. **Feature-Gated Release:** New validator binaries support `protocol_version + N`, with features disabled until explicitly activated via configuration flags.
2. **Independent Deployment:** Operators upgrade nodes asynchronously. The network continues operating at the active version.
3. **Readiness Signaling:** Upgraded validators emit a `ProtocolUpgradeSignal` transaction (Section 6.1) declaring support for the target version.
4. **Epoch Activation:** At each epoch boundary, the EpochManager evaluates readiness. If `≥ 2/3` of bonded stake (or `≥ 2/3` of permissioned validators in beta) signals readiness, the protocol version atomically advances.
5. **Feature Activation & Safe Exit:** New features activate instantly. Validators running outdated binaries fail-fast at the next consensus round and alert operators to upgrade.

**Safety Guarantees**

Old and new binaries produce **identical state under the active protocol version**. A network operating at version `N` can safely include nodes supporting up to `N + K` with zero behavioral divergence until the version flip. This eliminates chain-split risk and ensures consensus continuity during transitions.

**Safe-Mode Epoch Advance**

If `advance_epoch` encounters a fault (e.g., epoch-transition logic bug), `advance_epoch_safe_mode` executes instead. Only the minimum committee/version state advances; reward distribution and non-critical state transitions are deferred. Once a patched binary is deployed and `advance_epoch` succeeds, accumulated deferred operations resolve naturally over subsequent epochs.

**Permissioned-to-Decentralized Transition**

During permissioned-beta, the Foundation coordinates rolling upgrades directly with operators. At PoS activation (Phase 5+), upgrade authority transitions to validator consensus voting. The Foundation recuses itself from voting on proposals it originates, maintaining strict separation of operational and governance authority.


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