The final release of the Ethereum 2.0 spec version 0.1 has been announced by Danny Ryan, the Ethereum 2.0 coordinator. He said:

Major release centered on the integration of the IETF BLS standards into the eth2 spec. This release also contains a deep and much needed reorganization of files/directories

The rest of the changes are some minor optimizations and cleanups. Most of these are generally backward compatible, and all should be very straight forward to integrate.

v0.10.0 marks a stable target for Phase 0 for multi-client testnets and security reviews. We expect some revisions in February/March pending the results from each.

One of the Ethereum 2.0 clients, Ben Edgington of PegaSys, says that this version release is intended to be another frozen release, as the basis for both testnets and an audit. In addition to the audits related to the Beacon chain code, an audit of the deposit contract is currently happening. The ETH 2.0 clients are waiting for this version release before planning any multi-client testnet launch.

Though most of the stated changes are in regards to the signature standards, there are some changes proposed to the Beacon chain design itself. This release is an essential step towards the main full launch, with users and coders waiting for the audit reports, which might need a few further changes.

Edgington says:

Theres a 13,000 long queue of validators waiting to enter the Prysm testnet. New validators are onboarded at a maximum rate of 4 per epoch at the start, so thats two weeks of backlog by my calculations!

Few of these testnets have now upgraded to mainnet configuration, with some prospective stakers seemingly testing it all out. An ETH researcher at the Ethereum Foundation, Justin Drake, has announced the unofficial non-deadline of 30th July for the launch of the genesis block.

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Ethereum 2.0 spec version 0.1 release announced - FXStreet