Choose a version:
10% The original file has 64392 bytes (62.9k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 6588 bytes (6.4k, 10%).

After GZIP compression these minified files vary in size:
Boot
  2933 bytes (2.9k)
CDN, direct link
gzip -6 (default)
  2768 bytes (2.7k)
local copy
gzip -9
  2768 bytes (2.7k)
local copy
cdnjs
  2750 bytes (2.7k)
CDN, direct link
jsdelivr
  2748 bytes (2.7k)
CDN, direct link
libdeflate -12
  2722 bytes (2.7k)
local copy
pigz -11 -n
  2721 bytes (2.7k)
local copy
7zip -mx=9 -tgzip
  2720 bytes (2.7k)
local copy
kzip -s0 -rn -b0
  2718 bytes (2.7k)
local copy
Zopfli
  2716 bytes (2.7k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/react/react-16.0.0.min.js

You will automatically get the smallest React 16.0.0 file, ETag caching is available and
if your browser doesn't support GZIP decompression then the uncompressed version will be sent.

Currently best Zopfli settings

Save 32 bytes by using my React 16.0.0 Zopfli version instead of the best available CDN (1.18% smaller than jsdelivr, 2716 vs. 2748 bytes):
You can use my super-compressed files for whatever purpose you like as long as you respect the library's original license agreement.
There are no restrictions from my side - but please avoid hot-linking if you run a high-traffic website.

These command-line settings yielded the best compression ratio so far (Linux version of zopfli-krzymod):
zopfli --i100000 --mb8 --mls16 --bsr25 --lazy --ohh

(found October 6, 2017)
Description Value Parameter
iterations 100000  --i100000
maximum blocks 8  --mb8
maximum length score 16  --mls16
block splitting recursion 25  --bsr25
lazy matching in LZ77 yes  --lazy
optimized Huffman headers yes  --ohh
initial random W for iterations 1  --rw1
initial random Z for iterations 2  --rz2

Verify file integrity

After decompression, my uncompressed files are identical to the original ones:

MD5:
curl --silent --compressed https://fb.me/react-16.0.0.min.js --location | md5sum
34f96ffc962a7deecc83037ccb582b58  -
curl --silent --compressed http://minime.stephan-brumme.com/files/react/react-16.0.0.min.zopfli.js.gz | md5sum
34f96ffc962a7deecc83037ccb582b58  -

SHA1:
curl --silent --compressed https://fb.me/react-16.0.0.min.js --location | sha1sum
800a4e49a31bea4147ca2b7d44ecd41788dac705  -
curl --silent --compressed http://minime.stephan-brumme.com/files/react/react-16.0.0.min.zopfli.js.gz | sha1sum
800a4e49a31bea4147ca2b7d44ecd41788dac705  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
Boot 2933 bytes 34f96ffc962a7deecc83037ccb582b58 September 27, 2017 @ 10:56
cdnjs 2750 bytes 34f96ffc962a7deecc83037ccb582b58 September 27, 2017 @ 01:04
jsdelivr 2748 bytes 34f96ffc962a7deecc83037ccb582b58 October 6, 2017 @ 13:35

Note: only the MD5 hashes are shown to keep things simple.

Other Versions

Available React versions at minime.stephan-brumme.com:

16.0.0,
15.6.2, 15.6.1, 15.6.0,
15.5.2, 15.5.1, 15.5.0,
15.4.2, 15.4.1, 15.4.0,
15.3.2, 15.3.1, 15.3.0,
15.2.1, 15.2.0,
15.1.0,
15.0.2, 15.0.1, 15.0.0,
0.14.8, 0.14.7, 0.14.6, 0.14.5, 0.14.4, 0.14.3, 0.14.2, 0.14.1, 0.14.0,
0.13.3, 0.13.2, 0.13.1, 0.13.0,
0.12.2, 0.12.1, 0.12.0,
0.11.2, 0.11.1, 0.11.0,
0.10.0

The project site contains an overview how well these versions were compressed.
Other interesting projects are AngularJS, BackboneJS, Bootstrap, D3, Dojo, Ember, jQuery, Knockout, lodash, Socket.IO, ThreeJS, UnderscoreJS and Vue.

Changelog

Best Zopfli parameters so far:
Size Improvement Parameters Found
2716 bytes -1 byte zopfli --i100000 --mls16 --bsr25 --lazy --ohh October 6, 2017 @ 14:00
2717 bytes zopfli --i100 --mls16 --bsr15 --lazy --ohh October 6, 2017 @ 13:43

If there are multiple parameter sets yielding the same compressed size, only the first one found is shown.

Most recent activity on October 6, 2017 @ 18:30.

Heatmaps

This Zopfli heatmap visualizes how compression changes when modifying the --bsr and --mls parameter.
Cell's contents is the best filesize achieved (in bytes, hover with mouse over cells to see number of iterations).

Good parameters are green, bad are red. The best and worst are bold as well.
The brightness of the blue background color indicates how many iterations were processed:
10,000, 100,000 or 1,000,000.
bsr \ mls
2 4 8 16 32 64 128 256 512 1024 2048 4096 8192 16384 32768
bsr \ mls
2 4 8 16 32 64 128 256 512 1024 2048 4096 8192 16384 32768
2716 2716 2717 2719 2717 2717 2717 2717 2717 2717 2716 2716 2716 2716 2716
2716 2716 2717 2717 2717 2717 2717 2717 2717 2717 2716 2716 2716 2716 2716
2716 2717 2717 2716 2718 2717 2717 2717 2717 2717 2716 2716 2716 2716 2716
2717 2717 2717 2718 2717 2717 2717 2717 2717 2717 2716 2716 2716 2716 2716
2717 2717 2717 2717 2717 2717 2717 2717 2717 2717 2716 2716 2716 2716 2716
2716 2717 2717 2718 2718 2717 2717 2717 2717 2717 2716 2716 2716 2716 2716
2716 2716 2717 2718 2718 2717 2717 2717 2717 2717 2716 2716 2716 2716 2716
2716 2716 2717 2717 2718 2717 2717 2717 2717 2717 2716 2716 2716 2716 2716
2716 2717 2717 2717 2718 2717 2717 2717 2717 2717 2716 2716 2716 2716 2716
2716 2717 2717 2716 2718 2717 2717 2717 2717 2717 2716 2716 2716 2716 2716
2716 2717 2717 2718 2717 2717 2717 2717 2717 2717 2716 2716 2716 2716 2716
2716 2717 2717 2716 2717 2717 2717 2717 2717 2717 2716 2716 2716 2716 2716
2716 2717 2717 2718 2718 2717 2717 2717 2717 2717 2716 2716 2716 2716 2716
2716 2717 2717 2718 2718 2717 2717 2717 2717 2717 2716 2716 2716 2716 2716
2716 2717 2717 2718 2718 2717 2717 2717 2717 2717 2716 2716 2716 2716 2716
2716 2717 2717 2718 2718 2717 2717 2717 2717 2717 2716 2716 2716 2716 2716
2716 2717 2717 2717 2718 2717 2717 2717 2717 2717 2716 2716 2716 2716 2716
2716 2717 2717 2718 2718 2717 2717 2717 2717 2717 2716 2716 2716 2716 2716
2716 2717 2717 2718 2718 2717 2717 2717 2717 2717 2716 2716 2716 2716 2716
2717 2717 2717 2718 2718 2717 2717 2717 2717 2717 2716 2716 2716 2716 2716
2717 2717 2717 2716 2717 2717 2717 2717 2717 2717 2716 2716 2716 2716 2716
2716 2717 2717 2718 2719 2717 2717 2717 2717 2717 2716 2716 2716 2716 2716
2716 2717 2717 2716 2718 2717 2717 2717 2717 2717 2716 2716 2716 2716 2716

Due to the Monte Carlo design of my search algorithm, not all parameters have reached the same number of iterations yet:
Iterations Min. Bytes Reduction Coverage
100 2717 bytes 100%
1,000 2717 bytes 100%
10,000 2716 bytes -1 byte 100%
100,000 2716 bytes 41.74%
1,000,000 2716 bytes 0.29%
10,000,000

KZIP has far less options available for tuning/optimization. I only played around with the number of blocks (parameter -n):
Blocks Min. Bytes Compared To Best Zopfli Compared To Best KZIP
2718 bytes +2 bytes (+0.07%)
2718 bytes +2 bytes (+0.07%)
2733 bytes +17 bytes (+0.63%) +15 bytes
2764 bytes +48 bytes (+1.77%) +46 bytes
2801 bytes +85 bytes (+3.13%) +83 bytes
2838 bytes +122 bytes (+4.49%) +120 bytes
2878 bytes +162 bytes (+5.96%) +160 bytes
2918 bytes +202 bytes (+7.44%) +200 bytes
2944 bytes +228 bytes (+8.39%) +226 bytes

Non-DEFLATE Algorithms

Archivers based on completely different compression algorithms often produce superior results.
Unfortunately, browsers only support gzip compression at the moment.
Algorithm Program Parameters Size Compared To Best Zopfli
Brotli (Wikipedia) brotli brotli -q 11 2438 bytes -278 bytes (-10.24%)
RAR (proprietary) RAR rar a -m5 -md64m -mc63:128t -mt1 2563 bytes -153 bytes (-5.63%)
ZSTD (Wikipedia) zstd zstd -19 2748 bytes +32 bytes (+1.18%)
LZMA2 (Wikipedia) xz xz -9 2792 bytes +76 bytes (+2.80%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 2884 bytes +168 bytes (+6.19%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 2886 bytes +170 bytes (+6.26%)
ZPAQ (Wikipedia) zpaq zpaq -method 69 3433 bytes +717 bytes (+26.40%)

Detailled Analysis

I wrote a DEFLATE decoder in Javascript. Click the button below to start a client-side analysis of the smallest gzipped files (may take a second):


Notes: pigz is a fast open source multi-threaded implementation of gzip written by one of the original authors of gzip.
However, when using compression level 11, pigz actually switches to the slower Zopfli algorithm and isn't multi-threaded anymore.
KrzyMOD's extensions to Zopfli offer the highest level of configuration and is therefore used for my brute-force search.
Ken Silverman wrote the closed-source KZIP compression program and Jonathon Fowler ported it to Linux.
Defluff was created by Joachim Henke; DeflOpt is a tool by Ben Jos Walbeehm.

website made by Stephan Brumme in 2015 and still improving in 2017.
all timestamps are displayed in central european time. see my changelog.
no flash, not even images or external css files - and everything squeezed into a single html file.
which was handsomely compressed before releasing it into the wild internet - obviously.

please visit my homepage and my blog, too.
email: minime (at) stephan-brumme.com