Athens was the first proposed protocol amendment for Tezos. Two proposals - “Athens A” and “Athens B” were injected by the development team, Nomadic Labs in February 2019.
Of the two proposals, Athens A sought to increase the gas limit and reduce the roll size required to bake from 10,000 tez to 8,000 tez. Athens B sought to just increase the gas limit. Athens A was autonomously activated onto the protocol in May 2019.
For a full list of changes be sure to read the corresponding blog post from Nomadic Labs and reflection by Jacob Arluck.
The Babylon proposal was injected in August 2019 with contributions by development teams Nomadic Labs, Cryptium Labs (Metastate), and Marigold.
Notable changes included a new consensus algorithm variant (Emmy+), addition of new Michelson features to aid smart contract developers, an account rehaul that enabled clearer distinction between tz and kt accounts, as well as refinements to the quorum formula and addition of a 5% proposed quorum threshold.
Babylon was autonomously activated onto the protocol in October 2019.
The Carthage proposal was injected in December 2019 with contributions by development teams Nomadic Labs and Cryptium Labs (Metastate).
Notable changes included increasing the gas limit per block and operation by 30%, improving the accuracy of the formula used for calculating baking and endorsing rewards, as well as several minor improvements to Michelson.
Carthage was autonomously activated onto the protocol in March 2020.
The Florence proposal was a joint effort from Nomadic Labs, Marigold, DaiLambda, and Tarides.
Florence's notable bug fixes and improvements are:
Increasing maximum operation size
Improved gas consumption for execution of more complex smart contracts
Changing intercontract calls to a depth first ordering, as opposed to breadth first
The elimination of the test chain activation
Baking Accounts were also included in the feature set, however, ongoing testing had uncovered some important and previously undocumented breaking changes in the Baking Account proposal. Baking Accounts should be postponed until a thorough audit of functionality is complete, or an alternative implementation produced. The version of Florence without Baking Accounts is considered a safer choice.
The Granada proposal injected in May of 2021 was a joint effort from Nomadic Labs, Marigold, TQ, Tarides and DaiLambda.
Granada contains several major improvements to the protocol, as well as numerous bug fixes and minor improvements:
Emmy*: will generally halve the time between blocks, from 60 seconds to 30 seconds, allows transactions to achieve significantly faster finality than under the previous consensus algorithm.
Liquidity Baking: will incentivize large amounts of decentralized liquidity provision between tez and tzBTC by minting a small amount of tez every block and depositing it inside of a constant product market making smart-contract.
Gas improvements: A number of substantial improvements to performance have been made, which in turn result in dramatic reductions in gas consumption. Improvements by a factor of 3 to 6 ( sometimes 8 ) have been improved.