Choose a version:
24% The original file has 170539 bytes (166.5k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 41326 bytes (40.4k, 24%).

After GZIP compression these minified files vary in size:
Microsoft
  18315 bytes (17.9k)
CDN, direct link
Boot
  16798 bytes (16.4k)
CDN, direct link
cdnjs
  14744 bytes (14.4k)
CDN, direct link
gzip -6 (default)
  14677 bytes (14.3k)
local copy
cdnhttps
  14655 bytes (14.3k)
CDN, direct link
gzip -9
  14653 bytes (14.3k)
local copy
7zip -mx=9 -tgzip
  14251 bytes (13.9k)
local copy
kzip -s0 -rn -b0
  14246 bytes (13.9k)
local copy
libdeflate -12
  14215 bytes (13.9k)
local copy
pigz -11 -n
  14207 bytes (13.9k)
local copy
Zopfli
  14197 bytes (13.9k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/knockout/knockout-2.1.0.min.js

You will automatically get the smallest Knockout 2.1.0 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 458 bytes by using my Knockout 2.1.0 Zopfli version instead of the best available CDN (3.23% smaller than cdnhttps, 14197 vs. 14655 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 --i10000 --mb8 --mls64 --bsr9 --lazy --ohh

(found September 18, 2015)
Description Value Parameter
iterations 10000  --i10000
maximum blocks 8  --mb8
maximum length score 64  --mls64
block splitting recursion 9  --bsr9
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 http://knockoutjs.com/downloads/knockout-2.1.0.js --location | md5sum
10fea18c666dbafc68cbff1464996427  -
curl --silent --compressed http://minime.stephan-brumme.com/files/knockout/knockout-2.1.0.min.zopfli.js.gz | md5sum
10fea18c666dbafc68cbff1464996427  -

SHA1:
curl --silent --compressed http://knockoutjs.com/downloads/knockout-2.1.0.js --location | sha1sum
90654270f2e1d4650a82d6087a50ce7e9b0e187b  -
curl --silent --compressed http://minime.stephan-brumme.com/files/knockout/knockout-2.1.0.min.zopfli.js.gz | sha1sum
90654270f2e1d4650a82d6087a50ce7e9b0e187b  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
Microsoft 18315 bytes 10fea18c666dbafc68cbff1464996427 (invalid)
Boot 16798 bytes 10fea18c666dbafc68cbff1464996427 (invalid)
cdnjs 14744 bytes 10fea18c666dbafc68cbff1464996427 (invalid)
cdnhttps 14655 bytes 10fea18c666dbafc68cbff1464996427 December 24, 2015 @ 07:33

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

Other Versions

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

3.4.2, 3.4.1, 3.4.0,
3.3.0,
3.2.0,
3.1.0,
3.0.0,
2.3.0,
2.2.1, 2.2.0,
2.1.0,
2.0.0,
1.2.1, 1.2.0,
1.1.2, 1.1.1, 1.1.0

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

Changelog

Best Zopfli parameters so far:
Size Improvement Parameters Found
14197 bytes -1 byte zopfli --i10000 --mls64 --bsr9 --lazy --ohh September 18, 2015 @ 09:31
14198 bytes -1 byte zopfli --i10000 --mls64 --bsr6 --lazy --ohh September 18, 2015 @ 09:19
14199 bytes -1 byte zopfli --i1000 --mls512 --bsr16 --lazy --ohh September 10, 2015 @ 11:54
14200 bytes zopfli --i100 --mls512 --bsr16 --lazy --ohh September 10, 2015 @ 11:35

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

Most recent activity on June 16, 2016 @ 14:39.

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 or 100,000.
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
14210 14202 14203 14201 14202 14200 14200 14203 14213 14204 14210 14209 14213 14210 14211
14203 14199 14203 14210 14201 14201 14199 14200 14199 14200 14202 14202 14209 14205 14210
14211 14210 14211 14211 14210 14198 14197 14213 14201 14199 14204 14203 14209 14211 14208
14213 14212 14213 14210 14197 14199 14213 14210 14203 14197 14199 14212 14199 14207 14209
14197 14212 14213 14210 14200 14199 14197 14212 14204 14197 14204 14204 14210 14211 14208
14213 14212 14214 14211 14203 14197 14212 14216 14201 14199 14204 14204 14209 14208 14208
14204 14199 14204 14199 14197 14200 14197 14197 14203 14198 14203 14203 14209 14208 14208
14213 14213 14210 14210 14212 14212 14197 14199 14203 14204 14204 14203 14208 14208 14209
14213 14213 14210 14199 14199 14199 14197 14197 14201 14204 14204 14204 14208 14208 14208
14210 14213 14210 14210 14212 14211 14213 14212 14203 14197 14204 14204 14210 14209 14210
14203 14199 14199 14199 14204 14197 14197 14197 14201 14202 14204 14204 14208 14207 14204
14212 14212 14213 14210 14197 14199 14213 14213 14201 14197 14204 14204 14208 14207 14207
14203 14199 14200 14204 14203 14197 14199 14197 14199 14199 14205 14203 14209 14205 14209
14211 14213 14213 14216 14215 14211 14213 14212 14203 14199 14203 14203 14208 14208 14209
14214 14199 14210 14199 14197 14200 14197 14199 14201 14199 14203 14204 14208 14203 14203
14211 14213 14213 14212 14199 14197 14213 14212 14197 14199 14204 14204 14208 14208 14208
14203 14204 14198 14199 14197 14199 14197 14199 14201 14197 14204 14204 14210 14208 14208
14214 14213 14211 14210 14212 14197 14197 14199 14197 14199 14204 14204 14209 14209 14207
14198 14213 14210 14210 14211 14211 14209 14210 14201 14197 14203 14204 14209 14209 14208
14213 14213 14210 14210 14203 14199 14199 14197 14199 14197 14199 14204 14208 14208 14208
14213 14213 14211 14210 14212 14212 14214 14211 14199 14197 14204 14204 14209 14209 14209
14211 14212 14211 14213 14212 14212 14197 14197 14199 14197 14204 14204 14209 14208 14208
14213 14200 14198 14211 14204 14210 14197 14197 14201 14206 14204 14204 14207 14209 14208

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 14200 bytes 100%
1,000 14199 bytes -1 byte 100%
10,000 14197 bytes -2 bytes 100%
100,000 14197 bytes 13.04%
1,000,000
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
14246 bytes +49 bytes (+0.35%)
14246 bytes +49 bytes (+0.35%)
14273 bytes +76 bytes (+0.54%) +27 bytes
14308 bytes +111 bytes (+0.78%) +62 bytes
14295 bytes +98 bytes (+0.69%) +49 bytes
14316 bytes +119 bytes (+0.84%) +70 bytes
14330 bytes +133 bytes (+0.94%) +84 bytes
14354 bytes +157 bytes (+1.11%) +108 bytes
14396 bytes +199 bytes (+1.40%) +150 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
RAR (proprietary) RAR rar a -m5 -md64m -mc63:128t -mt1 12273 bytes -1924 bytes (-13.55%)
ZPAQ (Wikipedia) zpaq zpaq -method 69 12705 bytes -1492 bytes (-10.51%)
Brotli (Wikipedia) brotli brotli -q 11 12964 bytes -1233 bytes (-8.68%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 13182 bytes -1015 bytes (-7.15%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 13773 bytes -424 bytes (-2.99%)
LZMA2 (Wikipedia) xz xz -9 14036 bytes -161 bytes (-1.13%)
ZSTD (Wikipedia) zstd zstd -19 14190 bytes -7 bytes (-0.05%)

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