# ZIP 255: Deployment of the NU6.1 Network Upgrade

Status: Final

Owners: Daira-Emma Hopwood

Snapshot: a34cfc091434275120ff017c92c3b50d3cef623a

Source date: 2026-10-16T02:56:04+01:00

[Source revision](https://github.com/zcash/zips/commit/a34cfc091434275120ff017c92c3b50d3cef623a)

[Official source](https://zips.z.cash/zip-0255) · [Source file](https://github.com/zcash/zips/blob/a34cfc091434275120ff017c92c3b50d3cef623a/zips/zip-0255.md) · [Discussion](https://github.com/zcash/zips/issues/1011)

Preamble

**ZIP**: 255

**Title**: Deployment of the NU6.1 Network Upgrade

**Owners**: [Daira-Emma Hopwood](mailto:daira@jacaranda.org)

**Credits**: Arya

**Status**: Final

**Category**: Consensus / Network

**Created**: 2025-05-06

**License**: MIT

**Discussions-To**: [https://github.com/zcash/zips/issues/1011](https://github.com/zcash/zips/issues/1011)

<a id="terminology"></a>

## Terminology

The key word "MUST" in this document is to be interpreted as described in
BCP 14 <a id="user-content-fnref-bcp14"></a>
[1](#user-content-fn-bcp14) when, and only when, it appears in all capitals.

The term "network upgrade" in this document is to be interpreted as described
in ZIP 200. <a id="user-content-fnref-zip-0200"></a>
[2](#user-content-fn-zip-0200)

The character § is used when referring to sections of the Zcash Protocol
Specification. <a id="user-content-fnref-protocol"></a>
[3](#user-content-fn-protocol)

The terms "Mainnet" and "Testnet" are to be interpreted as described in
§ 3.12 ‘Mainnet and Testnet’. <a id="user-content-fnref-protocol-networks"></a>
[4](#user-content-fn-protocol-networks)

<a id="abstract"></a>

## Abstract

This proposal defines the deployment of the NU6.1 network upgrade.

<a id="specification"></a>

## Specification

<a id="nu6-1-deployment"></a>

### NU6.1 deployment

The primary sources of information about NU6.1 consensus protocol changes are:

- The Zcash Protocol Specification <a id="user-content-fnref-protocol-2"></a>
  [3](#user-content-fn-protocol).

- ZIP 200: Network Upgrade Mechanism <a id="user-content-fnref-zip-0200-2"></a>
  [2](#user-content-fn-zip-0200).

- ZIP 271: Deferred Dev Fund Lockbox Disbursement <a id="user-content-fnref-zip-0271"></a>
  [5](#user-content-fn-zip-0271).

- ZIP 1016: Community And Coinholder Funding Model <a id="user-content-fnref-zip-1016"></a>
  [6](#user-content-fn-zip-1016).

The network handshake and peer management mechanisms defined in ZIP 201
<a id="user-content-fnref-zip-0201"></a>
[7](#user-content-fn-zip-0201) also apply to this upgrade.

The following network upgrade constants <a id="user-content-fnref-zip-0200-3"></a>
[2](#user-content-fn-zip-0200) are defined for the
NU6.1 upgrade:

CONSENSUS_BRANCH_ID
: `0x4DEC4DF0`

ACTIVATION_HEIGHT (NU6.1)
: Testnet: 3536500
: Mainnet: 3146400

MIN_NETWORK_PROTOCOL_VERSION (NU6.1)
: Testnet: `170130`
: Mainnet: `170140`

For each network (Testnet and Mainnet), nodes compatible with NU6.1 activation
on that network MUST advertise a network protocol version that is greater
than or equal to the MIN_NETWORK_PROTOCOL_VERSION (NU6.1) for that activation.

<a id="backward-compatibility"></a>

### Backward compatibility

Prior to the network upgrade activating on each network, NU6.1 and pre-NU6.1
nodes are compatible and can connect to each other. However, NU6.1 nodes will
have a preference for connecting to other NU6.1 nodes, so pre-NU6.1 nodes will
gradually be disconnected in the run up to activation.

Once the network upgrades, even though pre-NU6.1 nodes can still accept the
numerically larger protocol version used by NU6.1 as being valid, NU6.1 nodes
will always disconnect peers using lower protocol versions.

<a id="references"></a>

## References

<a id="footnote-label"></a>

### Footnotes

1. [Information on BCP 14 — "RFC 2119: Key words for use in RFCs to Indicate Requirement Levels" and "RFC 8174: Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words"](https://www.rfc-editor.org/info/bcp14) [↩](#user-content-fnref-bcp14)

2. [ZIP 200: Network Upgrade Mechanism](/zip/200) [↩](#user-content-fnref-zip-0200) [↩2](#user-content-fnref-zip-0200-2) [↩3](#user-content-fnref-zip-0200-3)

3. [Zcash Protocol Specification, Version 2025.6.0 or later](protocol/protocol.pdf) [↩](#user-content-fnref-protocol) [↩2](#user-content-fnref-protocol-2)

4. [Zcash Protocol Specification, Version 2025.6.0 [NU6.1 proposal]. Section 3.12: Mainnet and Testnet](protocol/protocol.pdf#networks) [↩](#user-content-fnref-protocol-networks)

5. [ZIP 271: Deferred Dev Fund Lockbox Disbursement](/zip/271) [↩](#user-content-fnref-zip-0271)

6. [ZIP 1016: Community and Coinholder Funding Model](/zip/1016) [↩](#user-content-fnref-zip-1016)

7. [ZIP 201: Network Peer Management for Overwinter](/zip/201) [↩](#user-content-fnref-zip-0201)

## Citation relationships

Cites: [ZIP 200](https://zip-tools-web.harpocrates.workers.dev/zip/200), [ZIP 201](https://zip-tools-web.harpocrates.workers.dev/zip/201), [ZIP 271](https://zip-tools-web.harpocrates.workers.dev/zip/271), [ZIP 1016](https://zip-tools-web.harpocrates.workers.dev/zip/1016)

Cited by: [ZIP 214](https://zip-tools-web.harpocrates.workers.dev/zip/214), [ZIP 256](https://zip-tools-web.harpocrates.workers.dev/zip/256), [ZIP 271](https://zip-tools-web.harpocrates.workers.dev/zip/271)