diff --git a/packages/gradle-plugin/react-native-gradle-plugin/src/main/kotlin/com/facebook/react/ReactPlugin.kt b/packages/gradle-plugin/react-native-gradle-plugin/src/main/kotlin/com/facebook/react/ReactPlugin.kt
index 890edb58bd86..f3b5072dce93 100644
--- a/packages/gradle-plugin/react-native-gradle-plugin/src/main/kotlin/com/facebook/react/ReactPlugin.kt
+++ b/packages/gradle-plugin/react-native-gradle-plugin/src/main/kotlin/com/facebook/react/ReactPlugin.kt
@@ -95,7 +95,7 @@ class ReactPlugin : Plugin<Project> {
         val versionAndGroupStrings =
             readVersionAndGroupStrings(project, propertiesFile, hermesVersionPropertiesFile)
         configureDependencies(project, versionAndGroupStrings)
-        configureRepositories(project, versionAndGroupStrings.isNightly)
+        configureRepositories(project, versionAndGroupStrings)
       }
 
       configureReactNativeNdk(project, extension)
diff --git a/packages/gradle-plugin/react-native-gradle-plugin/src/main/kotlin/com/facebook/react/utils/DependencyUtils.kt b/packages/gradle-plugin/react-native-gradle-plugin/src/main/kotlin/com/facebook/react/utils/DependencyUtils.kt
index 4b4ffd0c1dd2..3b52d55d4659 100644
--- a/packages/gradle-plugin/react-native-gradle-plugin/src/main/kotlin/com/facebook/react/utils/DependencyUtils.kt
+++ b/packages/gradle-plugin/react-native-gradle-plugin/src/main/kotlin/com/facebook/react/utils/DependencyUtils.kt
@@ -31,6 +31,7 @@ import org.gradle.api.artifacts.repositories.MavenArtifactRepository
 internal object DependencyUtils {
   private const val REACT_NATIVE_MAVEN_MIRROR_URL = "https://repo.reactnative.dev/maven2"
   private const val REACT_NATIVE_MAVEN_MIRROR_ENABLED_ENV = "RCT_REACT_NATIVE_MAVEN_MIRROR_ENABLED"
+  private const val UNPUBLISHED_MAVEN_VERSION = "1000.0.0"
 
   internal data class Coordinates(
       val versionString: String,
@@ -124,6 +125,41 @@ internal object DependencyUtils {
     }
   }
 
+  /**
+   * Configures repositories without asking remote repositories for versions that are known to be
+   * unpublished.
+   */
+  fun configureRepositories(project: Project, coordinates: Coordinates) {
+    configureRepositories(project, coordinates.isNightly)
+
+    project.rootProject.allprojects { eachProject ->
+      eachProject.repositories.withType(MavenArtifactRepository::class.java).configureEach { repo ->
+        if (repo.url.scheme != "file") {
+          repo.content { content ->
+            if (!coordinates.versionString.isMavenArtifactVersionPublished()) {
+              setOf(DEFAULT_INTERNAL_REACT_PUBLISHING_GROUP, coordinates.reactGroupString)
+                  .forEach { group ->
+                    content.excludeVersion(group, "react-native", UNPUBLISHED_MAVEN_VERSION)
+                    content.excludeVersion(group, "react-android", UNPUBLISHED_MAVEN_VERSION)
+                  }
+            }
+            if (!coordinates.hermesVersionString.isMavenArtifactVersionPublished()) {
+              setOf(
+                      DEFAULT_INTERNAL_REACT_PUBLISHING_GROUP,
+                      DEFAULT_INTERNAL_HERMES_PUBLISHING_GROUP,
+                      coordinates.hermesGroupString,
+                  )
+                  .forEach { group ->
+                    content.excludeVersion(group, "hermes-engine", UNPUBLISHED_MAVEN_VERSION)
+                    content.excludeVersion(group, "hermes-android", UNPUBLISHED_MAVEN_VERSION)
+                  }
+            }
+          }
+        }
+      }
+    }
+  }
+
   /**
    * This method takes care of configuring the resolution strategy for both the app and all the 3rd
    * party libraries which are auto-linked. Specifically it takes care of:
@@ -303,6 +339,9 @@ internal object DependencyUtils {
 
   internal fun String.isNightly(): Boolean = this.startsWith("0.0.0") || "-nightly-" in this
 
+  internal fun String.isMavenArtifactVersionPublished(): Boolean =
+      this != UNPUBLISHED_MAVEN_VERSION
+
   internal fun Project.exclusiveEnterpriseRepository() =
       when {
         hasProperty(SCOPED_EXCLUSIVE_ENTEPRISE_REPOSITORY) ->
diff --git a/packages/gradle-plugin/react-native-gradle-plugin/src/test/kotlin/com/facebook/react/utils/DependencyUtilsTest.kt b/packages/gradle-plugin/react-native-gradle-plugin/src/test/kotlin/com/facebook/react/utils/DependencyUtilsTest.kt
index fed57c2025c3..17aca0a4afbf 100644
--- a/packages/gradle-plugin/react-native-gradle-plugin/src/test/kotlin/com/facebook/react/utils/DependencyUtilsTest.kt
+++ b/packages/gradle-plugin/react-native-gradle-plugin/src/test/kotlin/com/facebook/react/utils/DependencyUtilsTest.kt
@@ -12,13 +12,17 @@ import com.facebook.react.utils.DependencyUtils.configureDependencies
 import com.facebook.react.utils.DependencyUtils.configureRepositories
 import com.facebook.react.utils.DependencyUtils.exclusiveEnterpriseRepository
 import com.facebook.react.utils.DependencyUtils.getDependencySubstitutions
+import com.facebook.react.utils.DependencyUtils.isMavenArtifactVersionPublished
 import com.facebook.react.utils.DependencyUtils.isNightly
 import com.facebook.react.utils.DependencyUtils.isReactNativeMavenMirrorEnabled
 import com.facebook.react.utils.DependencyUtils.mavenRepoFromURI
 import com.facebook.react.utils.DependencyUtils.mavenRepoFromUrl
 import com.facebook.react.utils.DependencyUtils.readVersionAndGroupStrings
 import com.facebook.react.utils.DependencyUtils.shouldAddJitPack
+import com.sun.net.httpserver.HttpServer
+import java.net.InetSocketAddress
 import java.net.URI
+import java.util.concurrent.atomic.AtomicInteger
 import org.assertj.core.api.Assertions.assertThat
 import org.gradle.api.artifacts.repositories.MavenArtifactRepository
 import org.gradle.testfixtures.ProjectBuilder
@@ -78,6 +82,41 @@ class DependencyUtilsTest {
         .isNotNull()
   }
 
+  @Test
+  fun configureRepositories_withUnpublishedVersion_doesNotQueryRemoteRepository() {
+    val requests = AtomicInteger()
+    val server = HttpServer.create(InetSocketAddress("127.0.0.1", 0), 0)
+    server.createContext("/") { exchange ->
+      requests.incrementAndGet()
+      exchange.sendResponseHeaders(404, -1)
+      exchange.close()
+    }
+    server.start()
+
+    try {
+      val project = createProject()
+      project.extensions.extraProperties.set(
+          "exclusiveEnterpriseRepository",
+          "http://127.0.0.1:${server.address.port}",
+      )
+      configureRepositories(project, DependencyUtils.Coordinates("1000.0.0", "4.5.6"))
+      (project.repositories.first() as MavenArtifactRepository).isAllowInsecureProtocol = true
+
+      val published = project.configurations.create("published")
+      project.dependencies.add(published.name, "com.facebook.react:react-android:0.88.0")
+      assertThat(runCatching { published.resolve() }.isFailure).isTrue()
+      assertThat(requests.get()).isGreaterThan(0)
+
+      requests.set(0)
+      val unpublished = project.configurations.create("unpublished")
+      project.dependencies.add(unpublished.name, "com.facebook.react:react-android:1000.0.0")
+      assertThat(runCatching { unpublished.resolve() }.isFailure).isTrue()
+      assertThat(requests.get()).isZero()
+    } finally {
+      server.stop(0)
+    }
+  }
+
   @Test
   fun configureRepositories_containsGoogleRepo() {
     val repositoryURI = URI.create("https://dl.google.com/dl/android/maven2/")
@@ -414,6 +453,32 @@ class DependencyUtilsTest {
     assertThat(project.configurations.first().resolutionStrategy.forcedModules.isEmpty()).isTrue()
   }
 
+  @Test
+  fun configureDependencies_withUnpublishedVersion_preservesResolutionStrategy() {
+    val project = createProject()
+
+    configureDependencies(project, DependencyUtils.Coordinates("1000.0.0", "4.5.6"))
+
+    val forcedModules = project.configurations.first().resolutionStrategy.forcedModules
+    assertThat(
+            forcedModules.any {
+              it.toString() == "com.facebook.react:react-android:1000.0.0"
+            },
+        )
+        .isTrue()
+    assertThat(forcedModules.any { it.toString() == "com.facebook.hermes:hermes-android:4.5.6" })
+        .isTrue()
+
+    val dependencySubstitutions =
+        getDependencySubstitutions(DependencyUtils.Coordinates("1000.0.0", "4.5.6"))
+    assertThat(
+            dependencySubstitutions.any {
+              it.second == "com.facebook.react:react-android:1000.0.0"
+            },
+        )
+        .isTrue()
+  }
+
   @Test
   fun configureDependencies_withVersionString_appliesResolutionStrategy() {
     val project = createProject()
@@ -577,6 +642,12 @@ class DependencyUtilsTest {
     assertThat(hermesVersionString).isEqualTo("1000.0.0")
   }
 
+  @Test
+  fun isMavenArtifactVersionPublished_withMainVersion_returnsFalse() {
+    assertThat("1000.0.0".isMavenArtifactVersionPublished()).isFalse()
+    assertThat("0.88.0".isMavenArtifactVersionPublished()).isTrue()
+  }
+
   @Test
   fun readVersionString_withNightlyVersionString_returnsSnapshotVersion() {
     val propertiesFile =
diff --git a/packages/react-native/scripts/cocoapods/__tests__/maven_mirror_flag-test.rb b/packages/react-native/scripts/cocoapods/__tests__/maven_mirror_flag-test.rb
index 9f75f25fd7ae..c5ed599ee714 100644
--- a/packages/react-native/scripts/cocoapods/__tests__/maven_mirror_flag-test.rb
+++ b/packages/react-native/scripts/cocoapods/__tests__/maven_mirror_flag-test.rb
@@ -5,6 +5,8 @@
 
 require "test/unit"
 require_relative "../utils.rb"
+require_relative "../rncore.rb"
+require_relative "../rndependencies.rb"
 require_relative "../../../sdks/hermes-engine/hermes-utils.rb"
 
 class MavenMirrorFlagTests < Test::Unit::TestCase
@@ -39,4 +41,31 @@ def test_mavenMirror_isDisabledWhenExplicitlySetToFalse
         assert_false(ReactNativePodsUtils.react_native_maven_mirror_enabled?)
         assert_false(react_native_maven_mirror_enabled?)
     end
+
+    def test_unpublishedVersion_skipsAllArtifactLookups
+        assert_false(ReactNativePodsUtils.maven_artifact_version_published?('1000.0.0'))
+        assert_false(ReactNativePodsUtils.artifact_exists?('https://repo.reactnative.dev/maven2/example/1000.0.0/example.tar.gz'))
+        assert_false(ReactNativePodsUtils.artifact_exists?('https://central.sonatype.com/example/1000.0.0-SNAPSHOT/example.tar.gz'))
+        assert_false(ReactNativeCoreUtils.release_artifact_exists('1000.0.0'))
+        assert_false(ReactNativeCoreUtils.nightly_artifact_exists('1000.0.0'))
+        assert_false(ReactNativeDependenciesUtils.release_artifact_exists('1000.0.0'))
+        assert_false(ReactNativeDependenciesUtils.nightly_artifact_exists('1000.0.0'))
+        assert_false(release_artifact_exists('1000.0.0'))
+        assert_false(hermes_artifact_exists('https://repo.reactnative.dev/maven2/example/1000.0.0/example.tar.gz'))
+
+        assert_equal(
+            ReactNativeCoreUtils.stable_tarball_urls('1000.0.0', :debug).first,
+            ReactNativeCoreUtils.stable_tarball_url('1000.0.0', :debug),
+        )
+        assert_equal(
+            ReactNativeDependenciesUtils.release_tarball_urls('1000.0.0', :debug).first,
+            ReactNativeDependenciesUtils.release_tarball_url('1000.0.0', :debug),
+        )
+        assert_equal(release_tarball_urls('1000.0.0', :debug).first, release_tarball_url('1000.0.0', :debug))
+    end
+
+    def test_releaseVersion_isPublished
+        assert_true(ReactNativePodsUtils.maven_artifact_version_published?('0.88.0'))
+        assert_true(ReactNativePodsUtils.maven_artifact_version_published?('1000.0.0-abcdef123'))
+    end
 end
diff --git a/packages/react-native/scripts/cocoapods/rncore.rb b/packages/react-native/scripts/cocoapods/rncore.rb
index e56ce29b8a15..f588ad771f0b 100644
--- a/packages/react-native/scripts/cocoapods/rncore.rb
+++ b/packages/react-native/scripts/cocoapods/rncore.rb
@@ -367,6 +367,8 @@ def self.stable_tarball_urls(version, build_type, dsyms = false)
     end
 
     def self.nightly_tarball_url(version, configuration, dsyms = false)
+        return "" if !ReactNativePodsUtils.maven_artifact_version_published?(version)
+
         artefact_coordinate = "react-native-artifacts"
         artefact_name = "reactnative-core-#{dsyms ? "dSYM-" : ""}#{configuration ? configuration : "debug"}.tar.gz"
         xml_url = "https://central.sonatype.com/repository/maven-snapshots/com/facebook/react/#{artefact_coordinate}/#{version}-SNAPSHOT/maven-metadata.xml"
@@ -469,6 +471,8 @@ def self.release_artifact_exists(version)
     end
 
     def self.nightly_artifact_exists(version)
+        return false if !ReactNativePodsUtils.maven_artifact_version_published?(version)
+
         return artifact_exists(nightly_tarball_url(version, :debug).gsub("\\", ""))
     end
 
diff --git a/packages/react-native/scripts/cocoapods/rndependencies.rb b/packages/react-native/scripts/cocoapods/rndependencies.rb
index c38755263963..eb4bde3b3cfe 100644
--- a/packages/react-native/scripts/cocoapods/rndependencies.rb
+++ b/packages/react-native/scripts/cocoapods/rndependencies.rb
@@ -250,6 +250,8 @@ def self.release_tarball_urls(version, build_type)
     end
 
     def self.nightly_tarball_url(version, build_type)
+        return "" if !ReactNativePodsUtils.maven_artifact_version_published?(version)
+
         artifact_coordinate = "react-native-artifacts"
         artifact_name = "reactnative-dependencies-#{build_type.to_s}.tar.gz"
         xml_url = "https://central.sonatype.com/repository/maven-snapshots/com/facebook/react/#{artifact_coordinate}/#{version}-SNAPSHOT/maven-metadata.xml"
@@ -377,6 +379,8 @@ def self.release_artifact_exists(version)
     end
 
     def self.nightly_artifact_exists(version)
+        return false if !ReactNativePodsUtils.maven_artifact_version_published?(version)
+
         return artifact_exists(nightly_tarball_url(version, :debug).gsub("\\", ""))
     end
 
diff --git a/packages/react-native/scripts/cocoapods/utils.rb b/packages/react-native/scripts/cocoapods/utils.rb
index a31cab7442f6..3038897c8545 100644
--- a/packages/react-native/scripts/cocoapods/utils.rb
+++ b/packages/react-native/scripts/cocoapods/utils.rb
@@ -15,6 +15,7 @@
 class ReactNativePodsUtils
     MAVEN_CENTRAL_REPOSITORY = "https://repo1.maven.org/maven2"
     REACT_NATIVE_MAVEN_MIRROR_REPOSITORY = "https://repo.reactnative.dev/maven2"
+    UNPUBLISHED_MAVEN_VERSION = "1000.0.0"
 
     # Opt-in removal of the legacy TurboModule and component interop layers. Both are
     # off by default and will become the default in a future React Native release.
@@ -49,6 +50,11 @@ def self.react_native_maven_mirror_enabled?()
         value.downcase != "false" && value != "0"
     end
 
+    def self.maven_artifact_version_published?(version)
+        # 1000.0.0 identifies a source checkout on main and is never published to Maven.
+        return version != UNPUBLISHED_MAVEN_VERSION
+    end
+
     def self.warn_if_not_on_arm64
         if SysctlChecker.new().call_sysctl_arm64() == 1 && !Environment.new().ruby_platform().include?('arm64')
             Pod::UI.warn 'Do not use "pod install" from inside Rosetta2 (x86_64 emulation on arm64).'
@@ -833,6 +839,9 @@ def self.resolve_use_frameworks(spec, header_mappings_dir: nil, module_name: nil
     # (DNS failure, no route, ...) the probe is left uncached so that a
     # transient hiccup doesn't permanently mark the artifact as missing.
     def self.artifact_exists?(tarball_url)
+        unpublished_version = Regexp.escape(UNPUBLISHED_MAVEN_VERSION)
+        return false if tarball_url.match?(%r{/#{unpublished_version}(?:-SNAPSHOT)?/})
+
         unless @@artifact_exists_cache.key?(tarball_url)
             # -L is used to follow redirects, useful for the nightlies
             # The url is wrapped in quotes to avoid escaping & and ?.
diff --git a/packages/react-native/scripts/ios-prebuild/__tests__/utils-test.js b/packages/react-native/scripts/ios-prebuild/__tests__/utils-test.js
new file mode 100644
index 000000000000..7d443bd217b1
--- /dev/null
+++ b/packages/react-native/scripts/ios-prebuild/__tests__/utils-test.js
@@ -0,0 +1,52 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @format
+ * @noflow
+ */
+
+'use strict';
+
+const {
+  computeNightlyTarballURL,
+  isMavenArtifactVersionPublished,
+} = require('../utils');
+
+describe('isMavenArtifactVersionPublished', () => {
+  it('rejects the unpublished main version', () => {
+    expect(isMavenArtifactVersionPublished('1000.0.0')).toBe(false);
+  });
+
+  it.each([
+    '0.88.0',
+    '0.89.0-nightly-20260909-abcdef123',
+    '1000.0.0-abcdef123',
+  ])('accepts published artifact version %s', version => {
+    expect(isMavenArtifactVersionPublished(version)).toBe(true);
+  });
+});
+
+describe('computeNightlyTarballURL', () => {
+  it('does not query snapshot metadata for the unpublished main version', async () => {
+    const originalFetch = globalThis.fetch;
+    globalThis.fetch = jest.fn();
+
+    try {
+      await expect(
+        computeNightlyTarballURL(
+          '1000.0.0',
+          'Debug',
+          'react',
+          'react-native-artifacts',
+          'reactnative-dependencies-debug.tar.gz',
+        ),
+      ).rejects.toThrow(/artifacts are not published/);
+      expect(globalThis.fetch).not.toHaveBeenCalled();
+    } finally {
+      globalThis.fetch = originalFetch;
+    }
+  });
+});
diff --git a/packages/react-native/scripts/ios-prebuild/hermes.js b/packages/react-native/scripts/ios-prebuild/hermes.js
index 7e20ddf4f978..8956337fd3f2 100644
--- a/packages/react-native/scripts/ios-prebuild/hermes.js
+++ b/packages/react-native/scripts/ios-prebuild/hermes.js
@@ -8,7 +8,11 @@
  * @format
  */
 
-const {createLogger, getMavenRepositoryUrls} = require('./utils');
+const {
+  createLogger,
+  getMavenRepositoryUrls,
+  isMavenArtifactVersionPublished,
+} = require('./utils');
 const {execSync} = require('node:child_process');
 const fs = require('node:fs');
 const path = require('node:path');
@@ -204,6 +208,10 @@ async function findExistingTarballUrl(
   version /*: string */,
   buildType /*: BuildFlavor */,
 ) /*: Promise<?string> */ {
+  if (!isMavenArtifactVersionPublished(version)) {
+    return null;
+  }
+
   const candidates = getTarballUrls(version, buildType);
   for (const url of candidates) {
     if (await hermesArtifactExists(url)) {
@@ -341,6 +349,11 @@ async function downloadHermesTarball(
     const tmpFile = `${artifactsPath}/hermes-ios.download`;
     try {
       fs.mkdirSync(artifactsPath, {recursive: true});
+      if (!isMavenArtifactVersionPublished(version)) {
+        throw new Error(
+          `Maven artifacts are not published for the development version ${version}`,
+        );
+      }
       hermesLog(`Downloading Hermes tarball from ${tarballUrl}`);
 
       const response /*: Response */ = await fetch(tarballUrl);
diff --git a/packages/react-native/scripts/ios-prebuild/reactNativeDependencies.js b/packages/react-native/scripts/ios-prebuild/reactNativeDependencies.js
index bcc325ee0ea6..50b279709373 100644
--- a/packages/react-native/scripts/ios-prebuild/reactNativeDependencies.js
+++ b/packages/react-native/scripts/ios-prebuild/reactNativeDependencies.js
@@ -14,6 +14,7 @@ const {
   computeNightlyTarballURL,
   createLogger,
   getMavenRepositoryUrls,
+  isMavenArtifactVersionPublished,
 } = require('./utils');
 const {execSync} = require('node:child_process');
 const fs = require('node:fs');
@@ -236,6 +237,10 @@ async function findExistingTarballUrl(
   version /*: string */,
   buildType /*: BuildFlavor */,
 ) /*: Promise<?string> */ {
+  if (!isMavenArtifactVersionPublished(version)) {
+    return null;
+  }
+
   const candidates = getTarballUrls(version, buildType);
   for (const url of candidates) {
     if (await reactNativeDependenciesArtifactExists(url)) {
@@ -401,6 +406,11 @@ async function downloadReactNativeDependenciesTarball(
     const tmpFile = `${artifactsPath}/reactnative-dependencies.download`;
     try {
       fs.mkdirSync(artifactsPath, {recursive: true});
+      if (!isMavenArtifactVersionPublished(version)) {
+        throw new Error(
+          `Maven artifacts are not published for the development version ${version}`,
+        );
+      }
       dependencyLog(
         `Downloading ReactNativeDependencies tarball from ${tarballUrl}`,
       );
diff --git a/packages/react-native/scripts/ios-prebuild/utils.js b/packages/react-native/scripts/ios-prebuild/utils.js
index 036b398f750d..13e2aefe2213 100644
--- a/packages/react-native/scripts/ios-prebuild/utils.js
+++ b/packages/react-native/scripts/ios-prebuild/utils.js
@@ -17,6 +17,7 @@ const path = require('node:path');
 const MAVEN_CENTRAL_REPOSITORY = 'https://repo1.maven.org/maven2';
 const REACT_NATIVE_MAVEN_MIRROR_REPOSITORY =
   'https://repo.reactnative.dev/maven2';
+const UNPUBLISHED_MAVEN_VERSION = '1000.0.0';
 
 /**
  * Creates a folder if it does not exist
@@ -96,6 +97,12 @@ async function computeNightlyTarballURL(
   artifactCoordinate /*: string */,
   artifactName /*: string */,
 ) /*: Promise<string> */ {
+  if (!isMavenArtifactVersionPublished(version)) {
+    throw new Error(
+      `Maven artifacts are not published for the development version ${version}`,
+    );
+  }
+
   const xmlUrl = `https://central.sonatype.com/repository/maven-snapshots/com/facebook/${subGroup}/${artifactCoordinate}/${version}-SNAPSHOT/maven-metadata.xml`;
 
   const response = await fetch(xmlUrl);
@@ -156,6 +163,11 @@ function isReactNativeMavenMirrorEnabled() /*: boolean */ {
   return value.toLowerCase() !== 'false' && value !== '0';
 }
 
+function isMavenArtifactVersionPublished(version /*: string */) /*: boolean */ {
+  // 1000.0.0 identifies a source checkout on main and is never published to Maven.
+  return version !== UNPUBLISHED_MAVEN_VERSION;
+}
+
 module.exports = {
   createFolderIfNotExists,
   findFirst,
@@ -163,4 +175,5 @@ module.exports = {
   createLogger,
   computeNightlyTarballURL,
   getMavenRepositoryUrls,
+  isMavenArtifactVersionPublished,
 };
diff --git a/packages/react-native/scripts/spm/__tests__/download-spm-artifacts-test.js b/packages/react-native/scripts/spm/__tests__/download-spm-artifacts-test.js
index 3faaf5e8b087..2a24dbff8c5d 100644
--- a/packages/react-native/scripts/spm/__tests__/download-spm-artifacts-test.js
+++ b/packages/react-native/scripts/spm/__tests__/download-spm-artifacts-test.js
@@ -18,6 +18,7 @@ const {
   formatBytes,
   formatSpeed,
   hermesReleaseUrls,
+  isMavenArtifactVersionPublished,
   mavenRepositoryUrls,
   reactNativeMavenMirrorEnabled,
   resolveCacheSlotVersion,
@@ -377,6 +378,27 @@ describe('mavenRepositoryUrls', () => {
 // ---------------------------------------------------------------------------
 
 describe('release URL builders', () => {
+  it('preserves Maven URLs for the unpublished main version', () => {
+    expect(isMavenArtifactVersionPublished('1000.0.0')).toBe(false);
+    expect(rnCoreReleaseUrls('1000.0.0', 'debug')).toHaveLength(2);
+    expect(rnDepsReleaseUrls('1000.0.0', 'debug')).toHaveLength(2);
+    expect(hermesReleaseUrls('1000.0.0', 'debug')).toHaveLength(2);
+  });
+
+  it('does not probe Maven for the unpublished main version', async () => {
+    const originalFetch = globalThis.fetch;
+    globalThis.fetch = jest.fn();
+
+    try {
+      await expect(
+        exists(rnCoreReleaseUrls('1000.0.0', 'debug')[0]),
+      ).resolves.toBe(false);
+      expect(globalThis.fetch).not.toHaveBeenCalled();
+    } finally {
+      globalThis.fetch = originalFetch;
+    }
+  });
+
   it('rnCoreReleaseUrls builds a candidate per repository for the reactnative-core classifier', () => {
     const suffix =
       '/com/facebook/react/react-native-artifacts/0.85.0/' +
@@ -558,6 +580,20 @@ describe('resolveSnapshotUrl', () => {
     );
   });
 
+  it('does not query snapshot metadata for the unpublished main version', async () => {
+    globalThis.fetch = jest.fn();
+
+    await expect(
+      resolveSnapshotUrl(
+        '1000.0.0',
+        'react',
+        'react-native-artifacts',
+        'reactnative-core-debug.tar.gz',
+      ),
+    ).rejects.toThrow(/artifacts are not published/);
+    expect(globalThis.fetch).not.toHaveBeenCalled();
+  });
+
   it('throws when the metadata request fails', async () => {
     globalThis.fetch = routerFetch({
       'maven-metadata.xml': {ok: false, status: 500},
diff --git a/packages/react-native/scripts/spm/download-spm-artifacts.js b/packages/react-native/scripts/spm/download-spm-artifacts.js
index f84dc017b60b..82cb1dfc4ea9 100644
--- a/packages/react-native/scripts/spm/download-spm-artifacts.js
+++ b/packages/react-native/scripts/spm/download-spm-artifacts.js
@@ -141,9 +141,22 @@ function parseArgs(argv /*: Array<string> */) /*: DownloadArgs */ {
 const MAVEN_CENTRAL_REPOSITORY = 'https://repo1.maven.org/maven2';
 const REACT_NATIVE_MAVEN_MIRROR_REPOSITORY =
   'https://repo.reactnative.dev/maven2';
+const UNPUBLISHED_MAVEN_VERSION = '1000.0.0';
 const MAVEN_SNAPSHOT =
   'https://central.sonatype.com/repository/maven-snapshots';
 
+function isMavenArtifactVersionPublished(version /*: string */) /*: boolean */ {
+  // 1000.0.0 identifies a source checkout on main and is never published to Maven.
+  return version !== UNPUBLISHED_MAVEN_VERSION;
+}
+
+function isMavenArtifactUrlPublished(url /*: string */) /*: boolean */ {
+  return (
+    !url.includes(`/${UNPUBLISHED_MAVEN_VERSION}/`) &&
+    !url.includes(`/${UNPUBLISHED_MAVEN_VERSION}-SNAPSHOT/`)
+  );
+}
+
 /**
  * The mirror is ON unless RCT_REACT_NATIVE_MAVEN_MIRROR_ENABLED is
  * explicitly "false"/"0".
@@ -219,6 +232,12 @@ async function resolveSnapshotUrl(
   coordinate /*: string */,
   artifactName /*: string */,
 ) /*: Promise<string> */ {
+  if (!isMavenArtifactVersionPublished(version)) {
+    throw new Error(
+      `Maven artifacts are not published for the development version ${version}`,
+    );
+  }
+
   const metadataUrl =
     `${MAVEN_SNAPSHOT}/com/facebook/${subGroup}/${coordinate}/` +
     `${version}-SNAPSHOT/maven-metadata.xml`;
@@ -353,6 +372,10 @@ async function resolveLatestV1Version() /*: Promise<string> */ {
 }
 
 async function exists(url /*: string */) /*: Promise<boolean> */ {
+  if (!isMavenArtifactUrlPublished(url)) {
+    return false;
+  }
+
   try {
     // $FlowFixMe[incompatible-call] global fetch not in Flow stubs
     const res = await fetch(url, {method: 'HEAD'});
@@ -1510,6 +1533,7 @@ module.exports = {
   validateArtifactsCache,
   // Exposed for unit tests (pure / fetch-stubbable helpers).
   mavenRepositoryUrls,
+  isMavenArtifactVersionPublished,
   reactNativeMavenMirrorEnabled,
   rnCoreReleaseUrls,
   rnDepsReleaseUrls,
diff --git a/packages/react-native/sdks/hermes-engine/hermes-utils.rb b/packages/react-native/sdks/hermes-engine/hermes-utils.rb
index 71ef0481bbd4..ee13fc7c9240 100644
--- a/packages/react-native/sdks/hermes-engine/hermes-utils.rb
+++ b/packages/react-native/sdks/hermes-engine/hermes-utils.rb
@@ -9,6 +9,7 @@
 ENV_BUILD_FROM_SOURCE = "RCT_BUILD_HERMES_FROM_SOURCE"
 MAVEN_CENTRAL_REPOSITORY = "https://repo1.maven.org/maven2"
 REACT_NATIVE_MAVEN_MIRROR_REPOSITORY = "https://repo.reactnative.dev/maven2"
+UNPUBLISHED_HERMES_VERSION = "1000.0.0"
 
 # Memoized results of requests to the Maven repositories (mirror or central).
 # hermes-engine.podspec is evaluated several times during a single
@@ -356,6 +357,9 @@ def resolve_url_redirects(url)
 # Parameters
 # - tarball_url: the URL of the Hermes artifact to probe
 def hermes_artifact_exists(tarball_url)
+    unpublished_version = Regexp.escape(UNPUBLISHED_HERMES_VERSION)
+    return false if tarball_url.match?(%r{/#{unpublished_version}(?:-SNAPSHOT)?/})
+
     unless HERMES_ARTIFACT_EXISTS_CACHE.key?(tarball_url)
         # -L is used to follow redirects, useful for the nightlies
         # I also needed to wrap the url in quotes to avoid escaping & and ?.