# ZIP 205: Deployment of the Sapling 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-0205) · [Source file](https://github.com/zcash/zips/blob/a34cfc091434275120ff017c92c3b50d3cef623a/zips/zip-0205.rst)
Preamble
**ZIP**: 205
**Title**: Deployment of the Sapling Network Upgrade
**Owners**: [Daira-Emma Hopwood](mailto:daira@jacaranda.org)
**Credits**: Simon Liu
**Status**: Final
**Category**: Consensus / Network
**Created**: 2018-10-08
**License**: MIT
## Terminology
The key words "MUST" and "SHOULD" in this document are to be interpreted as described in BCP 14
[1](#fn1) when, and only when, they appear in all capitals.
The terms "consensus branch" and "network upgrade" in this document are to be interpreted as described in ZIP 200.
[2](#fn2)
The terms "Testnet" and "Mainnet" are to be interpreted as described in section 3.12 of the Zcash Protocol Specification
[3](#fn3).
The terms below are to be interpreted as follows:
**Sapling**:
Code-name for the second Zcash network upgrade, also known as Network Upgrade 1.
## Abstract
This proposal defines the deployment of the Sapling network upgrade. In addition, it describes a hard fork that occurred on Testnet to allow "minimum-difficulty" blocks.
## Specification
### Sapling deployment
The primary sources of information about Sapling consensus protocol changes are:
- The Zcash Protocol Specification
[4](#fn4).
- Transaction Signature Validation for Sapling
[5](#fn5).
- Network Upgrade Mechanism
[6](#fn6).
The network handshake and peer management mechanisms defined in
[7](#fn7) also apply to this upgrade.
The following network upgrade constants
[8](#fn8) are defined for the Sapling upgrade:
**CONSENSUS_BRANCH_ID**:
`0x76b809bb`
**ACTIVATION_HEIGHT (Sapling)**:
Testnet: 280000
Mainnet: 419200
On Testnet, Sapling had activated prior to this height, but that consensus branch was rolled back. A subsequent hard fork occurred on Testnet, changing the difficulty algorithm to accept "minimum-difficulty" blocks under certain conditions starting at block height 299188.
On both Mainnet and Testnet, Sapling-compatible nodes MUST advertise protocol version 170007 or later. The minimum peer protocol version that Sapling-compatible nodes will connect to, remains 170002.
Pre-Sapling nodes are defined as nodes advertising a protocol version less than 170007.
Approximately three days (defined in terms of block height) before the Sapling activation height, Sapling-compatible nodes will change the behaviour of their peer connection logic in order to prefer pre-Sapling peers for eviction from the set of peer connections.
```
/** The period before a network upgrade activates, where connections to upgrading peers are preferred (in blocks). */
static const int NETWORK_UPGRADE_PEER_PREFERENCE_BLOCK_PERIOD = 24 * 24 * 3;
```
The implementation is similar to that for Overwinter which was described in
[9](#fn9).
Once Sapling activates on Testnet or Mainnet, Sapling nodes SHOULD take steps to:
- reject new connections from pre-Sapling nodes;
- disconnect any existing connections to pre-Sapling nodes.
### Change to difficulty adjustment on Testnet
Section 7.6.3 of the Zcash Protocol Specification
[10](#fn10) describes the algorithm used to adjust the difficulty of a block (defined in terms of a "target threshold") based on the `nTime` and `nBits` fields of preceding blocks.
This algorithm changed on Testnet, starting from block 299188, to allow "minimum-difficulty" blocks. If the block time of a block from this height onward is greater than 15 minutes after that of the preceding block, then the block is a minimum-difficulty block. In that case its `nBits` field MUST be set to ToCompact(PoWLimit), where PoWLimit is the value defined for Testnet in section 5.3 of the Zcash Protocol Specification
[11](#fn11), and ToCompact is as defined in section 7.7.4 of that specification
[12](#fn12).
Note: a previous revision of this ZIP incorrectly said that only the target threshold of minimum-difficulty blocks is affected. In fact the `nBits` field is modified as well, and this affects difficulty adjustment for subsequent blocks.
This change does not affect Mainnet.
## Backward compatibility
Prior to the network upgrade activating, Sapling and pre-Sapling nodes are compatible and can connect to each other. However, Sapling nodes will have a preference for connecting to other Sapling nodes, so pre-Sapling nodes will gradually be disconnected in the run up to activation.
Once the network upgrades, even though pre-Sapling nodes can still accept the numerically larger protocol version used by Sapling as being valid, Sapling nodes will always disconnect peers using lower protocol versions.
## Support in zcashd
Support for Sapling consensus rules was implemented in zcashd version 2.0.0. The majority of support for RPC calls and persistence of Sapling z-addresses was implemented in version 2.0.1. Both of these versions advertise protocol version 170007.
## References
---
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)[↩︎](#fnref1)
2. [ZIP 200: Network Upgrade Mechanism](/zip/200)[↩︎](#fnref2)
3. [Zcash Protocol Specification, Version 2021.2.16. Section 3.12: Mainnet and Testnet](protocol/protocol.pdf#networks)[↩︎](#fnref3)
4. [Zcash Protocol Specification, Version 2021.2.16 or later](protocol/protocol.pdf)[↩︎](#fnref4)
5. [ZIP 243: Transaction Signature Validation for Sapling](/zip/243)[↩︎](#fnref5)
6. [ZIP 200: Network Upgrade Mechanism](/zip/200)[↩︎](#fnref6)
7. [ZIP 201: Network Peer Management for Overwinter](/zip/201)[↩︎](#fnref7)
8. [ZIP 200: Network Upgrade Mechanism](/zip/200)[↩︎](#fnref8)
9. [ZIP 201: Network Peer Management for Overwinter](/zip/201)[↩︎](#fnref9)
10. [Zcash Protocol Specification, Version 2021.2.16. Section 7.7.3: Difficulty adjustment](protocol/protocol.pdf#diffadjustment)[↩︎](#fnref10)
11. [Zcash Protocol Specification, Version 2021.2.16. Section 5.3: Constants](protocol/protocol.pdf#constants)[↩︎](#fnref11)
12. [Zcash Protocol Specification, Version 2021.2.16. Section 7.7.4: nBits conversion](protocol/protocol.pdf#nbits)[↩︎](#fnref12)
## 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 243](https://zip-tools-web.harpocrates.workers.dev/zip/243)
Cited by: [ZIP 173](https://zip-tools-web.harpocrates.workers.dev/zip/173), [ZIP 208](https://zip-tools-web.harpocrates.workers.dev/zip/208), [ZIP 210](https://zip-tools-web.harpocrates.workers.dev/zip/210), [ZIP 211](https://zip-tools-web.harpocrates.workers.dev/zip/211), [ZIP 213](https://zip-tools-web.harpocrates.workers.dev/zip/213), [ZIP 218](https://zip-tools-web.harpocrates.workers.dev/zip/218), [ZIP 243](https://zip-tools-web.harpocrates.workers.dev/zip/243), [ZIP 308](https://zip-tools-web.harpocrates.workers.dev/zip/308)