https://opensource.googleblog.com/2018/05/introducing-git-protocol-version-2.html

Today we announce Git protocol version 2, a major update of Git's wire protocol (how clones, fetches and pushes are communicated between clients and servers). This update removes one of the most inefficient parts of the Git protocol and fixes an extensibility bottleneck, unblocking the path to more wire protocol improvements in the future.

The protocol version 2 spec can be found here. The main improvements are:

• Server-side filtering of references

• Easy extensibility for new features like ref-in-want and fetching and pushing symrefs

• Simplified client handling of the http transport