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An "alpha/preview" version of BBRv2 is available under a "v2alpha" branch on GitHub. An implementation of BBRv2 for QUIC is included in the Chromium source as bbr2_sender.cc and bbr2_sender.h.
Other implementations
*BSD
Netflix has contributed Netflix is working on an implementation of BBR to FreeBSD. See the main/sys/netinet/tcp_stacks/bbr.c source file and the commented commit by Randall Stewart from September 2019.
Other
for FreeBSD. BBR has also been implemented for QUIC (including BBRv2, see above), and is in active use on Google's servers. Mark Claypool has written an implementation of BBR for ns-3, a popular network simulator.
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