While still valid, the substance behind Ethereum has changed, and will continue to, but will avoid making any disruptions to the operation of the network, while maintaining backwards compatibility, with the exception of the transition to Casper proof of stake. For past and planned changes, refer to here, except for Olympic and Frontier. Refer to here within the previous link for past hard forks. The original development roadmap that was laid out before Ethereum went live specified some of the following milestones:
- Prerelease step 0: Olympic testnet - launched May 2015 as announced here. The Olympic testnet phase saw a lot of major improvements, followed by Frontier which was launched immediately after.
- Release step 1.0: Frontier, launched 30 July 2015, starting from block 1. Here is an Ethereum blog post just before the launch, here and here is a wiki. More details are here. For a formal specification, refer to the Yellow Paper frontier branch here.
- Release step 2.0: Homestead, launched 14 March 2016 (Pi Day) at block number 1,150,000 as announced here. For changes in the Homestead release, see this EIP. Homestead marked the exit from a beta product to a stable release.
- Release step 2.1: DAO Hard Fork
- Release step 2.2: Tangerine Whistle, aka Anti-DoS, EIP 150
- Release step 2.3: Spurious Dragon, aka State-clearing, EIP 158/161, was released in Nov 2016. Spurious Dragon is aiming for Dapp developers as well as end users for limited categories of applications, and had a number of security enhancements.
- Release Step 3.0: Metropolis phase 1: Byzantium, October 16 2017 as announced here. Byzantium aims to introduce various privacy and functionality improvements. Details are here. For the Byzantium Hard Fork, refer to here, which is an archive link showing the Byzantium EIPs. Also, refer to here for a quick summary of Byzantium EIPs.
- Release Step 3.1: Metropolis phase 2: Constantinople, TBA, expected in 2018. Details on Metropolis are here. This archive link lists the deferred Constantinople EIPs. This is an archive link in case the EIPs list is changed in a way that does not breakdown EIPs into different releases, as is the case up until now.
- Release Step Four: Serenity, TBA. Serenity is meant to move from consensus through Proof-of-Work to Proof-of-Stake. Details are here and here, although the second post seems outdated as abstraction has moved forward to Constantinople.
- For other changes, refer to the the finalized list of EIPs.
- Further releases will focus on massive scalability increases through sharding as well as virtual machine improvements and other features, as detailed here.