diff --git a/chrome/app_shim/app_shim_controller.mm b/chrome/app_shim/app_shim_controller.mm
index de636b14..c3a78a7 100644
--- a/chrome/app_shim/app_shim_controller.mm
+++ b/chrome/app_shim/app_shim_controller.mm
@@ -293,6 +293,7 @@
        "UseIDNAContextJRules", "MojoBindingsInlineSLS",
        "MojoInlineMessagePayloads", "MojoIpcz", "MojoIpczMemV2",
        "MojoFixGeometricBufferGrowth", "UseAdHocSigningForWebAppShims",
+       "UseNSURLDataForGURLConversion",
        "SonomaAccessibilityActivationRefinements", "FeatureParamWithCache",
        "UseMachVouchers"});
 }
diff --git a/ios/chrome/browser/web/model/window_open_by_dom_egtest.mm b/ios/chrome/browser/web/model/window_open_by_dom_egtest.mm
index d59a009..fd89966 100644
--- a/ios/chrome/browser/web/model/window_open_by_dom_egtest.mm
+++ b/ios/chrome/browser/web/model/window_open_by_dom_egtest.mm
@@ -175,23 +175,15 @@
   [ChromeEarlGrey tapWebStateElementWithID:
                       @"webScenarioLocationReplaceInWindowOpenWithEmptyTarget"];
   [ChromeEarlGrey waitForMainTabCount:2];
-  // WebKit doesn't parse 'about:blank#hash' as about:blank with URL fragment.
-  // Instead, it percent encodes '#hash' and considers 'blank%23hash' as the
-  // resource identifier. Nevertheless, the '#' is significant in triggering the
-  // edge case in the bug. TODO(crbug.com/41414501): Change back to '#'.
-  // Since about scheme URLs are also trimmed to about:blank, check the url
-  // directly instead.
-  //
-  // TODO(crbug.com/40932726): Confirm the expected behavior of [ChromeEarlGrey
-  // webStateLastCommittedURL] here. After https://crrev.com/c/4823237, this
-  // returns empty URL ("").
-  DCHECK_EQ("", [ChromeEarlGrey webStateLastCommittedURL]);
-  // And confirm the location bar and focused omnibox are empty.
+  DCHECK_EQ(GURL("about:blank#hash"),
+            [ChromeEarlGrey webStateLastCommittedURL]);
+  // And confirm the location bar shows "about:blank".
   [[EarlGrey selectElementWithMatcher:chrome_test_util::DefocusedLocationView()]
-      assertWithMatcher:chrome_test_util::LocationViewEmpty()];
+      assertWithMatcher:chrome_test_util::LocationViewContainingText(
+                            "about:blank")];
   [ChromeEarlGreyUI focusOmnibox];
   [[EarlGrey selectElementWithMatcher:chrome_test_util::Omnibox()]
-      assertWithMatcher:chrome_test_util::OmniboxText("")];
+      assertWithMatcher:chrome_test_util::OmniboxText("about:blank")];
   [OmniboxEarlGrey defocusOmnibox];
 }
 
diff --git a/net/base/apple/url_conversions.mm b/net/base/apple/url_conversions.mm
index 8f38979..16481f1 100644
--- a/net/base/apple/url_conversions.mm
+++ b/net/base/apple/url_conversions.mm
@@ -6,10 +6,64 @@
 
 #import <Foundation/Foundation.h>
 
+#include "base/containers/fixed_flat_map.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/strings/escape.h"
+#include "base/strings/sys_string_conversions.h"
+#include "net/base/features.h"
 #include "url/gurl.h"
 #include "url/url_canon.h"
 
+namespace {
+
+// Schemes that are tracked in the Net.Apple.NSURL.DataMismatch.Scheme
+// histogram. These values are persisted to logs. Entries should not be
+// renumbered and numeric values should never be reused.
+enum class Scheme {
+  kUnknown = 0,
+  kOther = 1,
+  kAbout = 2,
+  kBlob = 3,
+  kContent = 4,
+  kData = 5,
+  kFile = 6,
+  kFileSystem = 7,
+  kFtp = 8,
+  kHttp = 9,
+  kHttps = 10,
+  kMailto = 11,
+  kTel = 12,
+  kMaxValue = kTel,
+};
+
+Scheme SchemeForURL(NSURL* url) {
+  NSString* scheme = [url scheme];
+  if (!scheme) {
+    return Scheme::kUnknown;
+  }
+
+  static constexpr auto kSchemeMap =
+      base::MakeFixedFlatMap<std::string_view, Scheme>({
+          {"about", Scheme::kAbout},
+          {"blob", Scheme::kBlob},
+          {"content", Scheme::kContent},
+          {"data", Scheme::kData},
+          {"file", Scheme::kFile},
+          {"filesystem", Scheme::kFileSystem},
+          {"ftp", Scheme::kFtp},
+          {"http", Scheme::kHttp},
+          {"https", Scheme::kHttps},
+          {"mailto", Scheme::kMailto},
+          {"tel", Scheme::kTel},
+      });
+
+  std::string lower_scheme = base::SysNSStringToUTF8([scheme lowercaseString]);
+  auto it = kSchemeMap.find(lower_scheme);
+  return it != kSchemeMap.end() ? it->second : Scheme::kOther;
+}
+
+}  // namespace
+
 namespace net {
 
 NSURL* NSURLWithGURL(const GURL& url) {
@@ -45,10 +99,41 @@
 }
 
 GURL GURLWithNSURL(NSURL* url) {
-  if (url) {
-    return GURL(url.absoluteString.UTF8String);
+  if (!url) {
+    return GURL();
   }
-  return GURL();
+
+  std::string_view standard_url_string(url.absoluteString.UTF8String);
+
+  // Foundation sometimes encodes the URL in absoluteString (and all the
+  // NSURL accessors other than dataRepresentation), which is not what we want
+  // to pass to GURL. For example, 'about:blank#hash' becomes
+  // 'about:blank%23hash' in absoluteString, but remains 'about:blank#hash' in
+  // dataRepresentation.
+  if (base::FeatureList::IsEnabled(features::kUseNSURLDataForGURLConversion)) {
+    NSData* data = [url dataRepresentation];
+    if (data && data.length > 0) {
+      std::string_view data_url_string(
+          reinterpret_cast<const char*>(data.bytes), data.length);
+      bool mismatch = standard_url_string != data_url_string;
+      // TODO(crbug.com/474953367): Consider removing these histograms after
+      // evaluation.
+      UMA_HISTOGRAM_BOOLEAN("Net.Apple.NSURL.DataMismatch", mismatch);
+      if (mismatch) {
+        Scheme scheme = SchemeForURL(url);
+        UMA_HISTOGRAM_ENUMERATION("Net.Apple.NSURL.DataMismatch.Scheme",
+                                  scheme);
+
+        // For "about:" scheme, use the data representation to avoid the
+        // encoding issue.
+        if (scheme == Scheme::kAbout) {
+          return GURL(data_url_string);
+        }
+      }
+    }
+  }
+
+  return GURL(standard_url_string);
 }
 
 }  // namespace net
diff --git a/net/base/apple/url_conversions_fuzzer.mm b/net/base/apple/url_conversions_fuzzer.mm
new file mode 100644
index 0000000..b5ed948
--- /dev/null
+++ b/net/base/apple/url_conversions_fuzzer.mm
@@ -0,0 +1,34 @@
+// Copyright 2026 The Chromium Authors
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "net/base/apple/url_conversions.h"
+
+#import <Foundation/Foundation.h>
+#include <stddef.h>
+#include <stdint.h>
+
+#include "base/check_op.h"
+#include "base/strings/sys_string_conversions.h"
+#include "url/gurl.h"
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
+  @autoreleasepool {
+    NSString* string = [[NSString alloc] initWithBytes:data
+                                                length:size
+                                              encoding:NSUTF8StringEncoding];
+    if (!string) {
+      return 0;
+    }
+
+    NSURL* url = [NSURL URLWithString:string];
+    if (url) {
+      GURL gurl_from_nsurl = net::GURLWithNSURL(url);
+      GURL gurl_from_string = GURL(base::SysNSStringToUTF8(string));
+      // A CHECK comparing gurl_from_nsurl gurl_from_string would not be
+      // useful because there are simply too many differences.
+      (void)(gurl_from_nsurl == gurl_from_string);
+    }
+  }
+  return 0;
+}
diff --git a/net/base/features.cc b/net/base/features.cc
index 40c72fd9..de9b6ab8 100644
--- a/net/base/features.cc
+++ b/net/base/features.cc
@@ -704,4 +704,8 @@
 
 BASE_FEATURE(kUseLockFreeX509Verification, base::FEATURE_DISABLED_BY_DEFAULT);
 
+#if BUILDFLAG(IS_APPLE)
+BASE_FEATURE(kUseNSURLDataForGURLConversion, base::FEATURE_ENABLED_BY_DEFAULT);
+#endif  // BUILDFLAG(IS_APPLE)
+
 }  // namespace net::features
diff --git a/net/base/features.h b/net/base/features.h
index 48f1da6e..7937e27 100644
--- a/net/base/features.h
+++ b/net/base/features.h
@@ -748,6 +748,12 @@
 // lock-free certificate verification mechanism.
 NET_EXPORT BASE_DECLARE_FEATURE(kUseLockFreeX509Verification);
 
+#if BUILDFLAG(IS_APPLE)
+// If enabled, the GURL conversion for NSURLs will use the data representation
+// of the URL if it differs from the absolute string.
+NET_EXPORT BASE_DECLARE_FEATURE(kUseNSURLDataForGURLConversion);
+#endif  // BUILDFLAG(IS_APPLE)
+
 }  // namespace net::features
 
 #endif  // NET_BASE_FEATURES_H_
diff --git a/tools/metrics/histograms/enums.xml b/tools/metrics/histograms/enums.xml
index b8e69607..e77590b 100644
--- a/tools/metrics/histograms/enums.xml
+++ b/tools/metrics/histograms/enums.xml
@@ -21734,6 +21734,22 @@
   <int value="8" label="H2 pings"/>
 </enum>
 
+<enum name="NSURLScheme">
+  <int value="0" label="Unknown"/>
+  <int value="1" label="Other"/>
+  <int value="2" label="about"/>
+  <int value="3" label="blob"/>
+  <int value="4" label="content"/>
+  <int value="5" label="data"/>
+  <int value="6" label="file"/>
+  <int value="7" label="filesystem"/>
+  <int value="8" label="ftp"/>
+  <int value="9" label="http"/>
+  <int value="10" label="https"/>
+  <int value="11" label="mailto"/>
+  <int value="12" label="tel"/>
+</enum>
+
 <enum name="NTPHistoryClustersModuleDisplayLayout">
   <int value="0" label="Not displayed"/>
   <int value="1" label="Layout 1"/>
diff --git a/tools/metrics/histograms/metadata/net/histograms.xml b/tools/metrics/histograms/metadata/net/histograms.xml
index 43a4bd6..884e70e 100644
--- a/tools/metrics/histograms/metadata/net/histograms.xml
+++ b/tools/metrics/histograms/metadata/net/histograms.xml
@@ -1494,6 +1494,29 @@
   </summary>
 </histogram>
 
+<histogram name="Net.Apple.NSURL.DataMismatch" enum="Boolean"
+    expires_after="2026-06-01">
+  <owner>[email protected]</owner>
+  <owner>[email protected]</owner>
+  <summary>
+    Records whether [NSURL dataRepresentation] and absoluteString give different
+    results during GURL conversion. Recorded each time the helper GURLWithNSURL
+    is called. This helps evaluate if switching to dataRepresentation is safe.
+  </summary>
+</histogram>
+
+<histogram name="Net.Apple.NSURL.DataMismatch.Scheme" enum="NSURLScheme"
+    expires_after="2026-06-01">
+  <owner>[email protected]</owner>
+  <owner>[email protected]</owner>
+  <summary>
+    Records the scheme of the URL when there is a mismatch between
+    absoluteString and dataRepresentation. Each time a ‘true’ value is recorded
+    for the Net.Apple.NSURL.DataMismatch histogram, one instance of this
+    histogram is recorded.
+  </summary>
+</histogram>
+
 <histogram name="Net.BlobFetch.ResponseNetErrorCode" enum="NetErrorCodes"
     expires_after="2026-06-28">
   <owner>[email protected]</owner>
diff --git a/net/base/apple/url_conversions_unittest.mm b/net/base/apple/url_conversions_unittest.mm
index db0c83a3..180299fc 100644
--- a/net/base/apple/url_conversions_unittest.mm
+++ b/net/base/apple/url_conversions_unittest.mm
@@ -2,10 +2,14 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#import "net/base/apple/url_conversions.h"
+
 #import <Foundation/Foundation.h>
 
 #include "base/strings/sys_string_conversions.h"
-#import "net/base/apple/url_conversions.h"
+#include "base/test/metrics/histogram_tester.h"
+#include "base/test/scoped_feature_list.h"
+#include "net/base/features.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "testing/gtest_mac.h"
 #include "url/gurl.h"
@@ -234,6 +238,33 @@
   EXPECT_EQ(nil, NSURLWithGURL(url));
 }
 
+TEST_F(URLConversionTest, TestGURLWithNSURLFeatureEnabled) {
+  base::HistogramTester histogram_tester;
+  base::test::ScopedFeatureList scoped_feature_list;
+  scoped_feature_list.InitAndEnableFeature(
+      features::kUseNSURLDataForGURLConversion);
+
+  NSURL* url = [NSURL URLWithString:@"about:blank#hash"];
+  GURL gurl = GURLWithNSURL(url);
+  EXPECT_EQ("about:blank#hash", gurl.spec());
+  histogram_tester.ExpectUniqueSample("Net.Apple.NSURL.DataMismatch", true, 1);
+}
+
+TEST_F(URLConversionTest, TestGURLWithNSURLFeatureDisabled) {
+  base::HistogramTester histogram_tester;
+  base::test::ScopedFeatureList scoped_feature_list;
+  scoped_feature_list.InitAndDisableFeature(
+      features::kUseNSURLDataForGURLConversion);
+
+  NSURL* url = [NSURL URLWithString:@"about:blank#hash"];
+  GURL gurl = GURLWithNSURL(url);
+  // If this test fails, it means Apple has fixed the bug in NSURL's
+  // absoluteString, and the kUseNSURLDataForGURLConversion workaround can be
+  // removed.
+  EXPECT_EQ("about:blank%23hash", gurl.spec());
+  histogram_tester.ExpectTotalCount("Net.Apple.NSURL.DataMismatch", 0);
+}
+
 }  // namespace
 
 }  // namespace net
diff --git a/net/BUILD.gn b/net/BUILD.gn
index ee245ae..669bb5f 100644
--- a/net/BUILD.gn
+++ b/net/BUILD.gn
@@ -4303,6 +4303,17 @@
   ]
 }
 
+if (is_apple) {
+  fuzzer_test("net_url_conversions_fuzzer") {
+    sources = [ "base/apple/url_conversions_fuzzer.mm" ]
+    deps = [
+      "//base",
+      "//net",
+    ]
+    frameworks = [ "Foundation.framework" ]
+  }
+}
+
 if (is_linux || is_chromeos) {
   fuzzer_test("net_base_address_tracker_linux_fuzzer") {
     sources = [ "base/address_tracker_linux_fuzzer.cc" ]

diff --git a/net/base/apple/url_conversions_unittest.mm b/net/base/apple/url_conversions_unittest.mm
index db0c83a3..180299fc 100644
--- a/net/base/apple/url_conversions_unittest.mm
+++ b/net/base/apple/url_conversions_unittest.mm
@@ -2,10 +2,14 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#import "net/base/apple/url_conversions.h"
+
 #import <Foundation/Foundation.h>
 
 #include "base/strings/sys_string_conversions.h"
-#import "net/base/apple/url_conversions.h"
+#include "base/test/metrics/histogram_tester.h"
+#include "base/test/scoped_feature_list.h"
+#include "net/base/features.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "testing/gtest_mac.h"
 #include "url/gurl.h"
@@ -234,6 +238,33 @@
   EXPECT_EQ(nil, NSURLWithGURL(url));
 }
 
+TEST_F(URLConversionTest, TestGURLWithNSURLFeatureEnabled) {
+  base::HistogramTester histogram_tester;
+  base::test::ScopedFeatureList scoped_feature_list;
+  scoped_feature_list.InitAndEnableFeature(
+      features::kUseNSURLDataForGURLConversion);
+
+  NSURL* url = [NSURL URLWithString:@"about:blank#hash"];
+  GURL gurl = GURLWithNSURL(url);
+  EXPECT_EQ("about:blank#hash", gurl.spec());
+  histogram_tester.ExpectUniqueSample("Net.Apple.NSURL.DataMismatch", true, 1);
+}
+
+TEST_F(URLConversionTest, TestGURLWithNSURLFeatureDisabled) {
+  base::HistogramTester histogram_tester;
+  base::test::ScopedFeatureList scoped_feature_list;
+  scoped_feature_list.InitAndDisableFeature(
+      features::kUseNSURLDataForGURLConversion);
+
+  NSURL* url = [NSURL URLWithString:@"about:blank#hash"];
+  GURL gurl = GURLWithNSURL(url);
+  // If this test fails, it means Apple has fixed the bug in NSURL's
+  // absoluteString, and the kUseNSURLDataForGURLConversion workaround can be
+  // removed.
+  EXPECT_EQ("about:blank%23hash", gurl.spec());
+  histogram_tester.ExpectTotalCount("Net.Apple.NSURL.DataMismatch", 0);
+}
+
 }  // namespace
 
 }  // namespace net