UPDATED | October 29, 2018:
According to Zcash, the Sapling fork, originally expected today, was completed on October 28, 2018, at block 419,200.
ORIGINAL | October 28, 2018:
The Zcash blockchain is set to hard fork on October 29, 2018, upgrading the network to make shielded transactions less computationally heavy, thereby making its currency easier to use.
The Zcash blockchain and coin (ZEC) went live in October 2016 with a focus on privacy by using zero-knowledge proofs. Zcash was the first big application of zk-SNARKs, a variation of zero-knowledge proofs that allow them to be used in blockchains and reduce their size and the computational strain on the network.
The upcoming network upgrade for Zcash, titled "Sapling," introduces more efficiencies for the blockchain's signature shielded transactions, which it says will "pave the way for broad mobile, exchange and vendor adoption of Zcash shielded addresses."
Shielded transactions take more computational power to transact, validate, and record on a blockchain, making them difficult to support for "light" cryptocurrency users, like mobile users, and for exchanges.
Sapling's shielded transactions will create new Sapling z-addresses for users which are shorter and will improve privacy for the entire Zcash network. Zcash says:
"Payments involving the new Sapling z-addresses can be constructed in as little as a few seconds and with only 40 megabytes of memory. Exchanges, mobile wallet providers, vendors and other 3rd parties will now be able to support shielded addresses."
The Sapling update will separate the hardware that constructs Zcash zero-knowledge proofs from the hardware that signs for transactions: Per Zcash: "Enterprises can perform an inexpensive signature step in a trusted environment while allowing another computer, not trusted with the spending key, to construct the proof."
Sapling will also improve viewing keys so owners of shielded addresses can view incoming and outgoing transaction details without exposing their private spending key. This will mean transactions can also be shared securely with trusted third parties where compliance or audit checks are required.
Lastly, the new Sapling z-addresses have a feature that "allows trillions" of addresses to receive payments at the same time without additional costs. Exchanges and merchants will now be able to create large numbers of "distinct and unlinkable" z-addresses for clients.
Some of the Sapling upgrade will need to be phased, as existing "Sprout" addresses will continue to be supported but eventually retired; some gradual migration may be required to ultimately progress Zcash to a more shielded and usable network.
The technology developed by Zcash has long been of interest to Ethereum co-founder Vitalik Buterin. From the outset, speculation circulated about a collaboration between Ethereum and Zcash, stemming from a number of compliments passed between founders Buterin and Wilcox.
One of the results was a research project between Ethereum and Zcash developers in 2017.
In September 2018, discussions between the two chains used the word "merger," something Buterin dismissed before going on to openly deliberate the possibilities.
There are no real signs of a merger between the chains, however Zcash technology obviously remains of interest to Ethereum, which implemented zk-SNARKs capabilities as part of the Ethereum Byzantium upgrade.