Choose a version:
12% The original file has 54798 bytes (53.5k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 6563 bytes (6.4k, 12%).

After GZIP compression these minified files vary in size:
Boot
  2917 bytes (2.8k)
CDN
gzip -9
  2745 bytes (2.7k)
local copy
gzip -6 (default)
  2744 bytes (2.7k)
local copy
cdnjs
  2729 bytes (2.7k)
CDN
jsdelivr
  2724 bytes (2.7k)
CDN
libdeflate -12
  2699 bytes (2.6k)
local copy
7zip -mx=9 -tgzip
  2698 bytes (2.6k)
local copy
kzip -s0 -rn -b0
  2697 bytes (2.6k)
local copy
pigz -11 -n
  2696 bytes (2.6k)
local copy
Zopfli
  2692 bytes (2.6k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/react/react-16.1.0.min.js (or via HTTPS)

You will automatically get the smallest React 16.1.0 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 16.1.0 Zopfli version instead of the best available CDN (1.19% smaller than jsdelivr, 2692 vs. 2724 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 --i1000000 --mb8 --mls2 --bsr10 --lazy --ohh

(found November 9, 2017)
Description Value Parameter
iterations 1000000  --i1000000
maximum blocks 8  --mb8
maximum length score 2  --mls2
block splitting recursion 10  --bsr10
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-16.1.0.min.js --location | md5sum
c0012ec056f45508c85dd45a3bccd578  -
curl --silent --compressed https://minime.stephan-brumme.com/files/react/react-16.1.0.min.zopfli.js.gz | md5sum
c0012ec056f45508c85dd45a3bccd578  -

SHA1:
curl --silent --compressed https://fb.me/react-16.1.0.min.js --location | sha1sum
0fb5191cf610f7b5740626ebaa9fabc331867400  -
curl --silent --compressed https://minime.stephan-brumme.com/files/react/react-16.1.0.min.zopfli.js.gz | sha1sum
0fb5191cf610f7b5740626ebaa9fabc331867400  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
Boot 2917 bytes c0012ec056f45508c85dd45a3bccd578 November 14, 2017 @ 18:05
cdnjs 2729 bytes c0012ec056f45508c85dd45a3bccd578 November 9, 2017 @ 16:50
jsdelivr 2724 bytes c0012ec056f45508c85dd45a3bccd578 November 9, 2017 @ 17:09

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

Other Versions

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

16.5.2, 16.5.1, 16.5.0,
16.4.2, 16.4.1, 16.4.0,
16.3.2, 16.3.1, 16.3.0,
16.2.0,
16.1.1, 16.1.0, 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
2692 bytes -1 byte zopfli --i1000000 --mls2 --bsr10 --lazy --ohh November 9, 2017 @ 17:50
2693 bytes -1 byte zopfli --i100000 --mls2 --bsr10 --lazy --ohh November 9, 2017 @ 17:20
2694 bytes -1 byte zopfli --i1000 --mls2 --bsr10 --lazy --ohh November 9, 2017 @ 17:14
2695 bytes zopfli --i100 --mls8 --bsr18 --lazy --ohh November 9, 2017 @ 17:12

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

Most recent activity on November 14, 2017 @ 18:05.

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
2694 2694 2694 2694 2694 2694 2694 2694 2694 2694 2693 2694 2694 2694 2694
2694 2694 2694 2694 2694 2694 2694 2694 2694 2694 2693 2694 2700 2700 2700
2694 2694 2694 2694 2694 2694 2694 2694 2694 2694 2693 2700 2700 2700 2700
2694 2694 2694 2694 2694 2694 2694 2694 2694 2694 2693 2699 2699 2699 2699
2694 2694 2694 2694 2694 2694 2694 2694 2694 2694 2693 2694 2700 2700 2700
2694 2694 2694 2694 2694 2694 2694 2694 2694 2694 2693 2694 2699 2699 2699
2692 2694 2694 2694 2694 2694 2694 2694 2694 2694 2693 2699 2700 2700 2700
2694 2694 2694 2694 2694 2694 2694 2694 2694 2694 2693 2699 2699 2699 2699
2694 2694 2694 2694 2694 2694 2694 2694 2694 2694 2693 2694 2699 2699 2699
2694 2694 2694 2694 2694 2694 2694 2694 2694 2694 2693 2699 2699 2699 2699
2694 2694 2694 2694 2694 2694 2694 2694 2694 2694 2693 2694 2699 2699 2699
2694 2694 2694 2694 2694 2694 2694 2694 2694 2694 2693 2699 2698 2698 2698
2694 2694 2694 2694 2694 2694 2694 2694 2694 2694 2693 2694 2699 2699 2699
2694 2694 2694 2694 2694 2694 2694 2694 2694 2694 2693 2694 2700 2700 2700
2694 2694 2694 2694 2694 2694 2694 2694 2694 2694 2693 2694 2700 2700 2700
2694 2694 2694 2694 2694 2694 2694 2694 2694 2694 2693 2699 2699 2699 2699
2694 2694 2694 2694 2694 2694 2694 2694 2694 2694 2693 2700 2699 2699 2699
2694 2694 2694 2694 2694 2694 2694 2694 2694 2694 2693 2694 2699 2699 2699
2694 2694 2694 2694 2694 2694 2694 2694 2694 2694 2693 2694 2699 2699 2699
2694 2694 2694 2694 2694 2694 2694 2694 2694 2694 2693 2694 2700 2700 2700
2694 2694 2694 2694 2694 2694 2694 2694 2694 2694 2693 2694 2694 2694 2694
2694 2694 2694 2694 2694 2694 2694 2694 2694 2694 2693 2694 2700 2700 2700
2694 2694 2694 2694 2694 2694 2694 2694 2694 2694 2693 2699 2698 2698 2698

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 2695 bytes 100%
1,000 2694 bytes -1 byte 100%
10,000 2693 bytes -1 byte 100%
100,000 2693 bytes 6.96%
1,000,000 2692 bytes -1 byte 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
2697 bytes +5 bytes (+0.19%)
2697 bytes +5 bytes (+0.19%)
2709 bytes +17 bytes (+0.63%) +12 bytes
2730 bytes +38 bytes (+1.41%) +33 bytes
2758 bytes +66 bytes (+2.45%) +61 bytes
2798 bytes +106 bytes (+3.94%) +101 bytes
2835 bytes +143 bytes (+5.31%) +138 bytes
2875 bytes +183 bytes (+6.80%) +178 bytes
2899 bytes +207 bytes (+7.69%) +202 bytes

Non-DEFLATE Algorithms

Archivers based on completely different compression algorithms often produce superior results.
Unfortunately, browsers only support gzip compression at the moment.
However, support for Brotli is constantly growing - but your browser doesn't support it.
Algorithm Program Parameters Size Compared To Best Zopfli
Brotli (Wikipedia) brotli brotli -q 11 2412 bytes -280 bytes (-10.40%)
RAR (proprietary) RAR rar a -m5 -md64m -mc63:128t -mt1 2543 bytes -149 bytes (-5.53%)
Zstandard (Wikipedia) zstd zstd -19 2721 bytes +29 bytes (+1.08%)
LZMA2 (Wikipedia) xz xz -9 2776 bytes +84 bytes (+3.12%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 2863 bytes +171 bytes (+6.35%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 2904 bytes +212 bytes (+7.88%)
ZPAQ (Wikipedia) zpaq zpaq -method 69 3433 bytes +741 bytes (+27.53%)

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 2018.
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