Zcash's ($ZEC) Overwinter update went live today at block 347500. The protocol upgrade was split into two tiers, with the first tier being an opt-in upgrade and the second tier being advocacy and education. The Overwinter upgrade sets the foundation for the upcoming Sapling upgrade scheduled for the end of 2018. Some of Overwinter's features include transaction expiry, versioning, replay protection for network upgrades, performance enhancements, and others that can be found on the Overwinter Zcash Improvement Proposals (ZIP).