Google is beginning to implement support for HTTP/3 in its Chrome browser, the company announced in a blog post. The update will bring some additional performance improvements, mostly thanks to the implementation of QUIC as the transport protocol.
The Internet Engineering Task Force, or IETF, introduced HTTP/2 back in 2015, and one of the big improvements it brought along was support for multiplexing. However, it used TCP as the transport protocol, and the loss recovery mechanisms in TCP, so lost packets can still cause a delay in all of the active transactions. By adopting QUIC, HTTP/3 can further improve the transfer process, since lost packets only affect the transactions directly affected by them.
Google was the original developer of QUIC, but the protocol has been in the IETF's hands for some time and the IETF version of QUIC is now significantly different from Google's in-house one. So far, Google has only been supporting its own QUIC implementation while IETF worked on its version, but now that's changing. Google says that IETF QUIC "significantly outperforms HTTPS over TLS 1.3 over TCP". For example, Google search latency decreases by 2%, while YouTube rebuffer time is reduced by 9%.
As such, the company is enabling support for IETF QUIC in its browser, with 25% of users having it enabled from today. The implementation is based on draft 29, which isn't the most recent version, but there are no breaking changes in subsequent drafts, according to Google. What Google isn't adding yet is support for IETF QUIC 0-RTT, which will come later, and it promises even better performance once it's available.
HTTP/3 is yet to be finalized, and it's not clear as of yet when browsers will have a fully finalized implementation.