The Spiral Upgrade will be activated on block 19,250,000, which is estimated to arrive January 31st 2024.
Miners, exchanges and all node operators are encouraged to keep their software updated to the latest version of core-geth before the activation block to ensure a smooth transition.
A service has been published to monitor adoption of the new client software at https://etcnodes.org/fork/spiral.
Similar to previous upgrades on Ethereum Classic, the Spiral Hard Fork is a compatibility update that includes technical changes to a number of OPCODEs relevant to the network. The Spiral Upgrade will bring the ETC Network to parity with upstream EVM standards, facilitating contract development and migration.
MESS (ECBP1100) is also scheduled to deactivate coincidentally with the Spiral hard fork.
The technical specification of Spiral can be found at https://ecips.ethereumclassic.org/ECIPs/ecip-1109.