Atlantis is an upcoming hard fork for Ethereum Classic. The fork is currently planned for block height #8,500,000 (subject to change).
Although the fork is somewhat contentious, it isn’t expected to create two chains or tokens with value (like the BCH and BSV split), it is only meant to improve the Ethereum Classic network.
In simple terms, the changes (a set of EIPs or “Ethereum Improvement Proposals”) are aimed at speed, efficiency, and making the issuance rate more predictable.
Learn more about the hard fork here: Going to Atlantis: Ethereum Classic (ETC) ECIP-1054 Hard Fork.
“The proposed changes will “Enable the outstanding Ethereum Foundation Spurious Dragon and Byzantium network protocol upgrades on the Ethereum Classic network in a hard-fork code-named Atlantis to enable maximum compatibility across these networks.”