Network Upgrade Guide

We recommend all wallets, exchanges, and clients that accept/support Zcash to follow these guidelines to prepare for the upcoming network upgrade. Network upgrades on a bi-annual basis to maintain the Zcash network.

Below is general advice that applies to all network upgrades:

Keep your zcashd node updated

Check that you are running the latest stable version of zcashd

Version verifiability

Clearly state the version of Zcash in a place users can find it. Somewhere inside the client’s user interface, state the protocol name and version number (available from the getblockchaininfo method). This allows users to check what version of Zcash their client is running.

Pre-upgrade notification

Inform users that a network upgrade is happening before it happens. 4000 blocks (approximately a week) in advance, tell users a network upgrade is happening soon, and that transactions will be unavailable for about an hour at the activation block height.

Defensive transition

Disable the initiation of new transactions starting 48 blocks (approximately one hour) before the activation block-height. If a user sends a transaction right before the upgrade, it is likely to not make it onto the chain. This can cause user confusion and frustration.

Post-upgrade notification

Tell users when the upgrade has finished and re-enable initiation of transactions. Notify users with a message or at their next login after the network transition.


NU5 is the sixth major network upgrade for Zcash and a component of the Halo Arc product suite release. NU5 represents the continued evolution of our zk-SNARK technology stack and will move Zcash to the Halo proving system, removing the need for the trusted setup and upgrading the protocol’s underlying cryptography.

Consensus Branch ID change

See ZIP 252 for full details on the deployment of NU5.

Require Canonical Jubjub Point Encodings

ZIP 216 fixes an oversight in the implementation of the Sapling consensus rules, by rejecting all non-canonical representations of Jubjub points.

Orchard Shielded Protocol

ZIP 224 introduces a new shielded pool with spending keys and payment addresses that are amenable to future scalability improvements. New pools with separate privacy sets are instituted at major network upgrades to increase security of the monetary base.

New Transaction Version Format

ZIP 225 defines an update to the Zcash peer-to-peer transaction format to include support for data elements required to support the Orchard protocol. The new transaction format defines well-bounded regions of the serialized form to serve each of the existing pools of funds, and adds and describes a new region containing Orchard-specific elements.

Relay of Version 5 Transactions

ZIP 239 alters the peer-to-peer network protocol, adding a new inv message type which must be used for advertising V5 transactions. This ensures that network nodes cannot perform a denial-of-service attack on wallets that are submitting V5 transactions to the mempool.

Non-malleable Transaction IDs

ZIP 244 defines a new transaction digest algorithm for the NU5 network upgrade onward, in order to introduce non-malleable transaction identifiers that commit to all transaction data except for attestations to transaction validity.

Unified addresses

ZIP 316 defines a new future-proof Zcash address format that improves usability, increases the ease of interoperability, and supports shielding Zcash by default. UAs make Zcash easier to use by removing the complexity of multiple address types. This simplifies the user experience and increases interoperability between shielded-only applications and transparent-only applications.


Canopy is the fifth network upgrade for Zcash, coinciding with the first Zcash halving. Canopy will establish a new development fund for the next four years.

Consensus Branch ID change

See ZIP 251

Development Fund ZIPs

ZIP 207 and ZIP 214 are needed to establish a new development fund. ZIP 207 specifies a mechanism to support funding streams, distributed from a portion of the block subsidy for a specified range of block heights. ZIP 214 describes consensus rule changes interpreting the proposed structure of the Zcash Development Fund, which is to be enacted in Canopy and last for 4 years.

Disabling Addition of New Value to Sprout Pool

ZIP 211 disables the ability to add new value to the Sprout value pool balance. This takes a step toward being able to remove the Sprout protocol, thus reducing the overall complexity and attack surface of Zcash.

Sapling Ephemeral Secret to Recipient in Note Plaintext

ZIP 212 improves the security assumptions needed to ensure that diversified addresses are not linkable. It does this by introducing a new note plaintext format for Sapling Outputs in transactions.

Fix Ed25519 Validation Rules to Allow Batch Validation

ZIP 215 improves the validity criteria of Ed25519 signatures used in Sprout transactions by explicitly defining criteria and changing them to be compatible with batch validation.


Heartwood is the fourth network upgrade for Zcash and enables more third-party integrations and better privacy through shielded coinbase.

Consensus Branch ID change

See ZIP 250

Flyclient Support

Flyclient, specified through ZIP 221, enables efficient proofs of Proof-of-Work for light clients. In addition to enabling improved light-client wallets, this improves many cross-chain protocols. This ZIP specifies modifications to be made to the Zcash block header format to include Merkle Mountain Range (MMR) commitments.

Shielded Coinbase

ZIP 213 defines modifications to the Zcash consensus rules that enable coinbase funds to be mined to shielded Sapling addresses. It does not disable the use of transparent addresses in coinbase transactions.


Blossom is the third network upgrade for Zcash.

Shorter Block Target Spacing

This feature increases the frequency of blocks, allowing transactions to resolve faster. This will improve Zcash’s usability and increase how many transactions per hour the network can sustain while keeping transaction fees low. This feature has undergone a specification audit. It is currently being tested on testnet as part of the Blossom Network Upgrade Pipeline, before version 2.1.0 of zcashd supporting mainnet activation is released in September.

Consensus Branch ID change

See ZIP 206

Amount of FR to be paid in coinbase transaction

See ZIP 208 and Protocol Section 7.7

Function from block height to FR has changed

See ZIP 208 and Protocol Section 7.8


Sapling is a network upgrade that introduces significant efficiency improvements for shielded transactions that will pave the way for broad mobile, exchange and vendor adoption of Zcash shielded addresses.

Transaction formatting

All transactions must use the new transaction format from Sapling onwards. Make sure that you can parse these v4 transactions. Previous formats will not be valid after the Sapling upgrade, so if you create transactions, the v4 format must be used after the upgrade has activated (but not until then). Hardware wallets and SPV clients are particularly affected here.

See ZIP 243. Test vectors for ZIP 243 have been pushed and are being reviewed.

Shielded HD Wallets

All Sapling addresses will use hierarchical deterministic key generation according to ZIP 32 (keypath m/32'/133'/k' on mainnet). Transparent and Sprout addresses will still use traditional key generation.

See ZIP 32.

Also see Sapling Protocol Specification.

General Guidelines

Using zcashd unmodified

If you use the RPC as provided in the zcashd client, which is true for most exchanges and general users of Zcash, you must update your zcashd node to at least version 2.0.1.

For an updated list of specific parameter changes for Sapling in the zcashd wallet RPC, please see: Sapling RPC Updates v2.0.1 (PDF).

Additionally, Sapling introduces new parameters which must be downloaded by running the script. These new parameters are placed in the same directory as the older Sprout parameters.

Using custom code to create/sign/send transactions

If you manually create transactions, the following changes are critical. Reference section 7.1 of the Sapling specification for complete details:

  • The transactions version number MUST be 4.

  • The version group ID MUST be 0x892F2085.

  • At least one of tx_in_count, nShieldedSpend, and nJoinSplit MUST be nonzero.

  • If version ≥ 4 and nShieldedSpend + nShieldedOutput > 0 then:

    • Let bvk and SigHash be as defined in §4.12 ‘Balance and Binding Signature (Sapling)’;

    • bindingSig MUST represent a valid signature under the transaction binding verification key bvk of SigHash - i.e. BindingSig.Verifybvk(SigHash, bindingSig) = 1.

  • If version ≥ 4 and nShieldedSpend + nShieldedOutput = 0, then valueBalance MUST be 0.

  • A coinbase transaction MUST NOT have any JoinSplit descriptions, Spend description, or Output descriptions.

  • valueBalance MUST be in the range {-MAX_MONEY .. MAX_MONEY}.

In addition, consensus rules associated with each JoinSplit description (§7.2 ‘Encoding of JoinSplit Descriptions’) each Spend description (§7.3 ‘Encoding of Spend Descriptions’) and each Output description (§7.4 ‘Encoding of Output Descriptions’) MUST be followed.

Mining Pools

Mining pools running the Stratum protocol will have to make some changes as well.

The hashReserved field in the Stratum Protocol will have to be replaced by the hashFinalSaplingRoot field from the block header (§7.5 ‘Block Header’).


Sapling is currently activated on testnet. To test transactions you’ll want to follow the Testnet Guide. Alternatively, developers can use these features in regtest mode.


Overwinter is the first network upgrade for Zcash. Its purpose is strengthening the protocol for future network upgrades. It includes versioning, replay protection for network upgrades, performance improvements for transparent transactions, a new feature of transaction expiry, and more.

Overwinter activated successfully at block 347500, mined at June 25, 2018 20:42 UTC-04:00

Transaction formatting

All transactions must use the new transaction format from Overwinter and onwards. Make sure that you can parse these “v3” transactions (write a parser for them if you aren’t using our code). Previous formats will not be valid after the Overwinter upgrade, so if you create transactions, the “v3” format must be used after the upgrade has activated (but not until then). Hardware wallets and SPV clients are particularly affected here. See ZIPs 202 and 203 .

Transaction version number

The 4-byte transaction version will have its most significant bit set from Overwinter and onwards, for two-way replay protection of Overwinter and unambiguous transaction parsing of all current and future formats. For example, existing “v1” and “v2” transactions use version numbers “1” and “2”, but “v3” Overwinter transactions will use the unsigned version number “(1 << 31) | 3” in the transaction serialization format. See ZIP 202 .

Version group IDs

A transaction version will be uniquely paired with a version group ID to ensure unambiguous transaction parsing. For example, a “v3” transaction will always have the version group ID “0x03C48270” in its serialization format, even after future network upgrades. See ZIP 202 .

Branch IDs

Each network upgrade has an associated branch ID that identifies its consensus rules. For two-way replay protection, creating transactions will require the branch ID of the current chain tip when signing a transaction (in the BLAKE2b personalization field.) You can obtain the branch ID of any block height from the getblock API. See ZIP 200 .

Signature hashing

There are new SegWit-like features in this upgrade, such as transaction signatures committing to values of the inputs. We suggest reusing code from SegWit (e.g. for hashing transparent outputs) when implementing the new SignatureHash function. See ZIP 143 .

Transaction expiry

We recommend that you do use the default expiry height (20 blocks/~1 hours) and follow these UX guidelines so that Zcash users can develop a consistent expectation of when Zcash transactions expire and what happens. Zee ZIP 203 .

This isn’t an exhaustive list of the changes. Look at the Overwinter Zcash Improvement Proposals (ZIPs) below for complete details on the changes that will be made. The five ZIPs cover network handshaking, transaction format, transaction expiry, signature hashing, and network upgrade mechanisms.

The network upgrade is coordinated via an on-chain activation mechanism.

Zcashd v1.1.0 (and future releases) running protocol version 170005 will activate Overwinter at block 347500 at which point only v3 transactions are processed. Older versions of Zcashd <= 1.0.14, running protocol versions <= 170004, will partition themselves away from the main network into a legacy chain.

Wipeout protection is provided by the new transaction format and signature hashing scheme. Blocks from the legacy chain will not be accepted by the upgraded network. That is, the upgraded network is permanent, and Zcashd v1.1.0 (and future releases) can not reorganize back to the older non-upgraded chain.

Common Issues


This error is simply saying that Overwinter has been activated and your client must be upgraded to the latest version. Upgrade your client and try again. If the issue persists try restarting the client. If this error is appearing on a third party app like a mobile wallet, please file a support request with the developer of the product and let us know in the #user-support channel on the community chat -


(Script evaluated without error but finished with a false/empty top stack element)

This error has been most commonly seen when using sendrawtransaction. This can be caused by a few things.

1. When creating raw transactions, the signrawtransaction step must be completed correctly. There is a field in signrawtransaction called prevtxs which can be seen here ( The prevtxs parameter is optional, but if it is specified, the amount parameter must also be specified. This amount is the total amount of the previous output. Prior to Overwinter the amount parameter was not required, this is a change between Overwinter and the previous version.

2. This issue can also arise in an edge case where a user is signing the transaction from an offline node. If this is the case the offline node must be synced to above the Overwinter activation height, block 347500.

Node sync is stuck before Overwinter activation height

This bug occurs when you are starting a fresh node or restarting a node that is not synced to above the Overwinter activation height (block 347500) and causes the node to sync very slowly. The bug has to do with your node incorrectly banning peer nodes. The end result is your node will sync very slowly as it will not be able to maintain as many connections to other nodes as usual.

This issue has been fixed in 2.0.0. Please update your client to 2.0.0 or above.