python
diff --git a/‎Doc/library/zlib.rst
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diff --git a/‎Doc/whatsnew/3.14.rst
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diff --git a/‎Lib/test/pythoninfo.py
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diff --git a/‎Misc/NEWS.d/next/Windows/2025-03-19-01-11-56.gh-issue-91349.pmtp-J.rst
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diff --git a/‎Misc/externals.spdx.json
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diff --git a/‎Modules/zlibmodule.c
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@@ -330,6 +330,18 @@ the following constants:
    .. versionadded:: 3.3
 
 
+.. data:: ZLIBNG_VERSION
+
+   The version string of the zlib-ng library that was used for building the
+   module if zlib-ng was used. When present, the :data:`ZLIB_VERSION` and
+   :data:`ZLIB_RUNTIME_VERSION` constants reflect the version of the zlib API
+   provided by zlib-ng.
+
+   If zlib-ng was not used to build the module, this constant will be absent.
+
+   .. versionadded:: 3.14
+
+
 .. seealso::
 
    Module :mod:`gzip`
 
@@ -1026,6 +1026,7 @@ zipinfo
   to produce reproducible output.
   (Contributed by Jiahao Li in :gh:`91279`.)
 
+
 .. Add improved modules above alphabetically, not here at the end.
 
 Optimizations
@@ -1078,6 +1079,18 @@ uuid
   (Contributed by Bénédikt Tran in :gh:`128150`.)
 
 
+zlib
+----
+
+* On Windows, ``zlib-ng`` is now used as the implementation of the
+  :mod:`zlib` module. This should produce compatible and comparable
+  results with better performance, though it is worth noting that
+  ``zlib.Z_BEST_SPEED`` (1) may result in significantly less
+  compression than the previous implementation (while also significantly
+  reducing the time taken to compress).
+  (Contributed by Steve Dower in :gh:`91349`.)
+
+
 Deprecated
 ==========
 
 
@@ -651,7 +651,7 @@ def collect_zlib(info_add):
     except ImportError:
         return
 
-    attributes = ('ZLIB_VERSION', 'ZLIB_RUNTIME_VERSION')
+    attributes = ('ZLIB_VERSION', 'ZLIB_RUNTIME_VERSION', 'ZLIBNG_VERSION')
     copy_attributes(info_add, zlib, 'zlib.%s', attributes)
 
 
 
@@ -0,0 +1,2 @@
+Replaces our copy of ``zlib`` with ``zlib-ng``, for performance improvements
+in :mod:`zlib`.
@@ -171,25 +171,25 @@
       "versionInfo": "5.2.5"
     },
     {
-      "SPDXID": "SPDXRef-PACKAGE-zlib",
+      "SPDXID": "SPDXRef-PACKAGE-zlib-ng",
       "checksums": [
         {
           "algorithm": "SHA256",
-          "checksumValue": "e3f3fb32564952006eb18b091ca8464740e5eca29d328cfb0b2da22768e0b638"
+          "checksumValue": "00bbd88709bc416cb96160ab61d3e1c8f76e106799af7328d0fe434dc7dd5004"
         }
       ],
-      "downloadLocation": "https://github.com/python/cpython-source-deps/archive/refs/tags/zlib-1.3.1.tar.gz",
+      "downloadLocation": "https://github.com/python/cpython-source-deps/archive/refs/tags/zlib-ng-2.2.4.tar.gz",
       "externalRefs": [
         {
           "referenceCategory": "SECURITY",
-          "referenceLocator": "cpe:2.3:a:zlib:zlib:1.3.1:*:*:*:*:*:*:*",
+          "referenceLocator": "cpe:2.3:a:zlib-ng:zlib-ng:2.2.4:*:*:*:*:*:*:*",
           "referenceType": "cpe23Type"
         }
       ],
       "licenseConcluded": "NOASSERTION",
-      "name": "zlib",
+      "name": "zlib-ng",
       "primaryPackagePurpose": "SOURCE",
-      "versionInfo": "1.3.1"
+      "versionInfo": "2.2.4"
     }
   ],
   "spdxVersion": "SPDX-2.3"
 
@@ -2101,6 +2101,12 @@ zlib_exec(PyObject *mod)
                      PyUnicode_FromString(zlibVersion())) < 0) {
         return -1;
     }
+#ifdef ZLIBNG_VERSION
+    if (PyModule_Add(mod, "ZLIBNG_VERSION",
+                     PyUnicode_FromString(ZLIBNG_VERSION)) < 0) {
+        return -1;
+    }
+#endif
     if (PyModule_AddStringConstant(mod, "__version__", "1.0") < 0) {
         return -1;
     }
Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,2 @@`
	`1`	+Replaces our copy of ``zlib`` with ``zlib-ng``, for performance improvements
	`2`	+in :mod:`zlib`.
Original file line number	Diff line number	Diff line change
`@@ -171,25 +171,25 @@`
`171`	`171`	`"versionInfo": "5.2.5"`
`172`	`172`	`},`
`173`	`173`	`{`
`174`		`- "SPDXID": "SPDXRef-PACKAGE-zlib",`
	`174`	`+ "SPDXID": "SPDXRef-PACKAGE-zlib-ng",`
`175`	`175`	`"checksums": [`
`176`	`176`	`{`
`177`	`177`	`"algorithm": "SHA256",`
`178`		`- "checksumValue": "e3f3fb32564952006eb18b091ca8464740e5eca29d328cfb0b2da22768e0b638"`
	`178`	`+ "checksumValue": "00bbd88709bc416cb96160ab61d3e1c8f76e106799af7328d0fe434dc7dd5004"`
`179`	`179`	`}`
`180`	`180`	`],`
`181`		`- "downloadLocation": "https://github.com/python/cpython-source-deps/archive/refs/tags/zlib-1.3.1.tar.gz",`
	`181`	`+ "downloadLocation": "https://github.com/python/cpython-source-deps/archive/refs/tags/zlib-ng-2.2.4.tar.gz",`
`182`	`182`	`"externalRefs": [`
`183`	`183`	`{`
`184`	`184`	`"referenceCategory": "SECURITY",`
`185`		`- "referenceLocator": "cpe:2.3:a:zlib:zlib:1.3.1:::::::*",`
	`185`	`+ "referenceLocator": "cpe:2.3:a:zlib-ng:zlib-ng:2.2.4:::::::*",`
`186`	`186`	`"referenceType": "cpe23Type"`
`187`	`187`	`}`
`188`	`188`	`],`
`189`	`189`	`"licenseConcluded": "NOASSERTION",`
`190`		`- "name": "zlib",`
	`190`	`+ "name": "zlib-ng",`
`191`	`191`	`"primaryPackagePurpose": "SOURCE",`
`192`		`- "versionInfo": "1.3.1"`
	`192`	`+ "versionInfo": "2.2.4"`
`193`	`193`	`}`
`194`	`194`	`],`
`195`	`195`	`"spdxVersion": "SPDX-2.3"`
Original file line number	Diff line number	Diff line change
`@@ -2101,6 +2101,12 @@ zlib_exec(PyObject *mod)`
`2101`	`2101`	`PyUnicode_FromString(zlibVersion())) < 0) {`
`2102`	`2102`	`return -1;`
`2103`	`2103`	`}`
	`2104`	`+#ifdef ZLIBNG_VERSION`
	`2105`	`+ if (PyModule_Add(mod, "ZLIBNG_VERSION",`
	`2106`	`+ PyUnicode_FromString(ZLIBNG_VERSION)) < 0) {`
	`2107`	`+ return -1;`
	`2108`	`+ }`
	`2109`	`+#endif`
`2104`	`2110`	`if (PyModule_AddStringConstant(mod, "__version__", "1.0") < 0) {`
`2105`	`2111`	`return -1;`
`2106`	`2112`	`}`