Prior information is available on the releases page.
The ETH1 page lists Working Groups and areas of focus.
Constantinople is planned for Q1 of 2019. Planned date was originally January 16th, 2019, 12:00pm UTC. Now will activate February 25th, 2019, at the same time as Petersburgh, which de-activates EIP-1283.
Istanbul is planned for Q4 of 2019. Planned date is October 16th, 2019, 12:00pm UTC.
More details on the road to Istanbul.
Current discussion is on moving towards a 6-month cycle. Danno is leading discussion on a Cheesy Hardfork Schedule
Note: We are not using cheese names, they are annoying on purpose to force us to choose new names as part of the hardfork meta creation process!
See the ETH2 Specs Github Repo.
The ETH2 Project Management repo holds ongoing notes and meetings.