<s>
HTTP/3	B-Protocol
is	O
the	O
third	O
major	O
version	O
of	O
the	O
Hypertext	B-Protocol
Transfer	I-Protocol
Protocol	I-Protocol
used	O
to	O
exchange	O
information	O
on	O
the	O
World	O
Wide	O
Web	O
,	O
complementing	O
the	O
widely-deployed	O
HTTP/1.1	B-Protocol
and	O
HTTP/2	B-Protocol
.	O
</s>
<s>
Unlike	O
previous	O
versions	O
which	O
relied	O
on	O
the	O
well-established	O
TCP	B-Protocol
(	O
published	O
in	O
1974	O
)	O
,	O
HTTP/3	B-Protocol
uses	O
QUIC	B-Protocol
,	O
a	O
multiplexed	B-Architecture
transport	B-Architecture
protocol	I-Architecture
built	O
on	O
UDP	B-Protocol
.	O
</s>
<s>
On	O
6	O
June	O
2022	O
,	O
IETF	O
published	O
HTTP/3	B-Protocol
as	O
a	O
Proposed	O
Standard	O
in	O
.	O
</s>
<s>
HTTP/3	B-Protocol
uses	O
similar	O
semantics	O
compared	O
to	O
earlier	O
revisions	O
of	O
the	O
protocol	O
,	O
including	O
the	O
same	O
request	O
methods	O
,	O
status	O
codes	O
,	O
and	O
message	O
fields	O
,	O
but	O
encodes	O
them	O
and	O
maintains	O
session	O
state	O
differently	O
.	O
</s>
<s>
However	O
,	O
partially	O
due	O
to	O
the	O
protocol	O
's	O
adoption	O
of	O
QUIC	B-Protocol
,	O
HTTP/3	B-Protocol
has	O
lower	O
latency	O
and	O
loads	O
more	O
quickly	O
in	O
real-world	O
usage	O
when	O
compared	O
with	O
previous	O
versions	O
:	O
in	O
some	O
cases	O
over	O
3×	O
faster	O
than	O
with	O
HTTP/1.1	B-Protocol
(	O
which	O
,	O
for	O
many	O
websites	O
,	O
is	O
the	O
only	O
HTTP	B-Protocol
version	O
deployed	O
)	O
.	O
</s>
<s>
HTTP/3	B-Protocol
is	O
supported	O
by	O
75%	O
of	O
tracked	O
web	O
browser	O
installations	O
(	O
and	O
81%	O
of	O
"	O
tracked	O
desktop	O
"	O
web	O
browsers	O
)	O
,	O
and	O
26%	O
of	O
the	O
top	O
10	O
million	O
websites	O
.	O
</s>
<s>
It	O
has	O
been	O
supported	O
by	O
Chromium	B-Language
(	O
and	O
derived	O
projects	O
including	O
Google	B-Application
Chrome	I-Application
,	O
Microsoft	B-Application
Edge	I-Application
,	O
Samsung	B-Application
Internet	I-Application
,	O
and	O
Opera	B-Application
)	O
since	O
April	O
2020	O
and	O
by	O
Mozilla	B-Application
Firefox	I-Application
since	O
May	O
2021	O
.	O
</s>
<s>
Safari	B-Application
14	O
(	O
on	O
macOS	B-Operating_System
Big	I-Operating_System
Sur	I-Operating_System
and	O
iOS	B-Operating_System
14	I-Operating_System
,	O
and	O
"	O
is	O
a	O
major	O
new	O
feature	O
in	O
iOS	B-Operating_System
15	I-Operating_System
"	O
;	O
for	O
apps	O
)	O
implemented	O
the	O
protocol	O
but	O
it	O
remains	O
disabled	O
by	O
default	O
.	O
</s>
<s>
HTTP/3	B-Protocol
originates	O
from	O
an	O
Internet	O
Draft	O
adopted	O
by	O
the	O
QUIC	B-Protocol
working	O
group	O
.	O
</s>
<s>
The	O
original	O
proposal	O
was	O
named	O
"	O
HTTP/2	B-Protocol
Semantics	O
Using	O
The	O
QUIC	B-Protocol
Transport	B-Architecture
Protocol	I-Architecture
"	O
,	O
and	O
later	O
renamed	O
"	O
Hypertext	B-Protocol
Transfer	I-Protocol
Protocol	I-Protocol
(	O
HTTP	B-Protocol
)	O
over	O
QUIC	B-Protocol
"	O
.	O
</s>
<s>
On	O
28	O
October	O
2018	O
in	O
a	O
mailing	O
list	O
discussion	O
,	O
Mark	O
Nottingham	O
,	O
Chair	O
of	O
the	O
IETF	O
HTTP	B-Protocol
and	O
QUIC	B-Protocol
Working	O
Groups	O
,	O
proposed	O
renaming	O
HTTP-over-QUIC	O
to	O
HTTP/3	B-Protocol
,	O
to	O
"	O
clearly	O
identify	O
it	O
as	O
another	O
binding	O
of	O
HTTP	B-Protocol
semantics	O
to	O
the	O
wire	O
protocol	O
 [ ... ] 	O
so	O
people	O
understand	O
its	O
separation	O
from	O
QUIC	B-Protocol
"	O
.	O
</s>
<s>
The	O
HTTP	B-Protocol
working	O
group	O
was	O
chartered	O
to	O
assist	O
the	O
QUIC	B-Protocol
working	O
group	O
during	O
the	O
design	O
of	O
HTTP/3	B-Protocol
,	O
then	O
assume	O
responsibility	O
for	O
maintenance	O
after	O
publication	O
.	O
</s>
<s>
Support	O
for	O
HTTP/3	B-Protocol
was	O
added	O
to	O
Chrome	B-Application
(	O
Canary	O
build	O
)	O
in	O
September	O
2019	O
and	O
then	O
eventually	O
reached	O
stable	O
builds	O
,	O
but	O
was	O
disabled	O
by	O
a	O
feature	O
flag	O
.	O
</s>
<s>
Firefox	B-Application
added	O
support	O
for	O
HTTP/3	B-Protocol
in	O
November	O
2019	O
through	O
a	O
feature	O
flag	O
and	O
started	O
enabling	O
it	O
by	O
default	O
in	O
April	O
2021	O
in	O
Firefox	B-Application
88	O
.	O
</s>
<s>
Experimental	O
support	O
for	O
HTTP/3	B-Protocol
was	O
added	O
to	O
Safari	B-Application
Technology	O
Preview	O
on	O
April	O
8	O
,	O
2020	O
and	O
was	O
included	O
with	O
Safari	B-Application
14	O
that	O
ships	O
with	O
iOS	B-Operating_System
14	I-Operating_System
and	O
macOS	B-Operating_System
11	I-Operating_System
,	O
but	O
it	O
's	O
still	O
disabled	O
by	O
default	O
as	O
of	O
Safari	B-Application
16	O
,	O
on	O
both	O
macOS	O
and	O
iOS	O
.	O
</s>
<s>
HTTP	B-Protocol
semantics	O
are	O
consistent	O
across	O
versions	O
:	O
the	O
same	O
request	O
methods	O
,	O
status	O
codes	O
,	O
and	O
message	O
fields	O
are	O
typically	O
applicable	O
to	O
all	O
versions	O
.	O
</s>
<s>
Both	O
HTTP/1.1	B-Protocol
and	O
HTTP/2	B-Protocol
use	O
TCP	B-Protocol
as	O
their	O
transport	O
.	O
</s>
<s>
HTTP/3	B-Protocol
uses	O
QUIC	B-Protocol
,	O
a	O
transport	B-Architecture
layer	I-Architecture
network	O
protocol	O
which	O
uses	O
user	B-Operating_System
space	I-Operating_System
congestion	O
control	O
over	O
the	O
User	B-Protocol
Datagram	I-Protocol
Protocol	I-Protocol
(	O
UDP	B-Protocol
)	O
.	O
</s>
<s>
The	O
switch	O
to	O
QUIC	B-Protocol
aims	O
to	O
fix	O
a	O
major	O
problem	O
of	O
HTTP/2	B-Protocol
called	O
"	O
head-of-line	B-Protocol
blocking	I-Protocol
"	O
:	O
because	O
the	O
parallel	O
nature	O
of	O
HTTP/2	B-Protocol
'	O
s	O
multiplexing	B-Architecture
is	O
not	O
visible	O
to	O
TCP	B-Protocol
's	O
loss	O
recovery	O
mechanisms	O
,	O
a	O
lost	O
or	O
reordered	O
packet	B-Protocol
causes	O
all	O
active	O
transactions	B-General_Concept
to	O
experience	O
a	O
stall	O
regardless	O
of	O
whether	O
that	O
transaction	O
was	O
impacted	O
by	O
the	O
lost	O
packet	B-Protocol
.	O
</s>
<s>
Because	O
QUIC	B-Protocol
provides	O
native	O
multiplexing	B-Architecture
,	O
lost	O
packets	B-Protocol
only	O
impact	O
the	O
streams	O
where	O
data	O
has	O
been	O
lost	O
.	O
</s>
<s>
Proposed	O
DNS	O
resource	O
records	O
SVCB	O
(	O
service	O
binding	O
)	O
and	O
HTTPS	B-Protocol
would	O
allow	O
connecting	O
without	O
first	O
receiving	O
the	O
Alt-Svc	O
header	O
via	O
previous	O
HTTP	B-Protocol
versions	O
,	O
therefore	O
removing	O
the	O
1	O
RTT	O
of	O
handshaking	O
of	O
TCP	B-Protocol
.	O
</s>
<s>
There	O
is	O
client	O
support	O
for	O
HTTPS	B-Protocol
resource	O
records	O
since	O
Firefox	B-Application
92	O
,	O
iOS	B-Operating_System
14	I-Operating_System
,	O
reported	O
Safari	B-Application
14	O
support	O
,	O
and	O
Chromium	B-Language
supports	O
it	O
behind	O
a	O
flag	O
.	O
</s>
<s>
HTTP/3	B-Protocol
makes	O
Transport	B-Architecture
Layer	I-Architecture
Security	O
(	O
TLS	O
)	O
mandatory	O
and	O
includes	O
it	O
through	O
QUIC	B-Protocol
,	O
which	O
uses	O
TLS	O
1.3	O
within	O
the	O
protocol	O
exchanges	O
.	O
</s>
<s>
TLS	O
can	O
be	O
upgraded	O
to	O
mutual	O
TLS	O
(	O
mTLS	O
)	O
by	O
using	O
certificates	O
for	O
Identity	O
together	O
with	O
authentication	O
and	O
authorization	O
,	O
with	O
open	O
source	O
implementations	O
of	O
QuicSec	O
enabling	O
a	O
smooth	O
transition	O
from	O
prior	O
versions	O
of	O
HTTP	B-Protocol
.	I-Protocol
</s>
<s>
+	O
Browser	O
support	O
for	O
HTTP/3BrowserVersion	O
implemented	O
(	O
disabled	O
by	O
default	O
)	O
Version	O
shipped	O
(	O
enabled	O
by	O
default	O
)	O
CommentChromeStable	O
build	O
(	O
79	O
)	O
December	O
201987April	O
2020Earlier	O
versions	O
implemented	O
other	O
drafts	O
of	O
QUICEdgeStable	O
build	O
(	O
79	O
)	O
December	O
201987April	O
2020Edge	O
79	O
was	O
the	O
first	O
version	O
based	O
on	O
ChromiumFirefoxStable	O
build	O
(	O
72.0.1	O
)	O
January	O
202088April	O
2021SafariStable	O
build	O
(	O
14.0	O
)	O
September	O
202016.4March	O
2023Apple	O
is	O
testing	O
HTTP/3	B-Protocol
support	O
on	O
some	O
Safari	B-Application
users	O
starting	O
with	O
Safari	B-Application
16.4	O
.	O
</s>
<s>
On	O
7	O
June	O
2021	O
,	O
LiteSpeed	B-Protocol
Web	I-Protocol
Server	I-Protocol
(	O
and	O
OpenLiteSpeed	O
)	O
6.0.2	O
was	O
released	O
and	O
became	O
the	O
first	O
version	O
to	O
enable	O
HTTP/3	B-Protocol
by	O
default	O
.	O
</s>
<s>
Caddy	B-Language
web	O
server	O
v2.6.0	O
(	O
released	O
20	O
September	O
2022	O
)	O
has	O
HTTP/3	B-Protocol
enabled	O
by	O
default	O
.	O
</s>
<s>
Nginx	B-Operating_System
support	O
for	O
HTTP/3	B-Protocol
is	O
being	O
worked	O
on	O
.	O
</s>
<s>
A	O
technology	O
preview	O
of	O
nginx	B-Operating_System
with	O
HTTP/3	B-Protocol
support	O
was	O
released	O
in	O
June	O
2020	O
.	O
</s>
<s>
Binary	O
packages	O
of	O
nginx	B-Operating_System
with	O
HTTP3	B-Protocol
support	O
have	O
been	O
released	O
in	O
February	O
2023	O
.	O
</s>
<s>
Cloudflare	B-Application
distributes	O
a	O
patch	O
for	O
nginx	B-Operating_System
that	O
integrates	O
the	O
quiche	O
HTTP/3	B-Protocol
library	O
into	O
it	O
.	O
</s>
<s>
Microsoft	B-Application
IIS	I-Application
support	O
for	O
HTTP/3	B-Protocol
is	O
enabled	O
natively	O
with	O
Windows	O
Server	O
2022/Windows	O
11	O
.	O
</s>
<s>
HAProxy	B-Language
supports	O
HTTP/3	B-Protocol
over	O
QUIC	B-Protocol
since	O
version	O
2.6	O
released	O
on	O
31	O
May	O
2022	O
.	O
</s>
<s>
TLS	O
1.3	O
is	O
built	O
into	O
the	O
QUIC	B-Protocol
protocol	I-Protocol
and	O
required	O
for	O
HTTP3	B-Protocol
.	O
</s>
