diff --git a/common/changes/@microsoft/rush/sennyeya-fix-injected-dep-hash_2026-03-17-14-17.json b/common/changes/@microsoft/rush/sennyeya-fix-injected-dep-hash_2026-03-17-14-17.json
new file mode 100644
index 00000000000..494238eee0f
--- /dev/null
+++ b/common/changes/@microsoft/rush/sennyeya-fix-injected-dep-hash_2026-03-17-14-17.json
@@ -0,0 +1,11 @@
+{
+  "changes": [
+    {
+      "comment": "Fixes a bug where the injected dependency state hash updated on devDependency changes that wouldn't impact the lockfile.",
+      "type": "none",
+      "packageName": "@microsoft/rush"
+    }
+  ],
+  "packageName": "@microsoft/rush",
+  "email": "aramissennyeydd@users.noreply.github.com"
+}
\ No newline at end of file
diff --git a/libraries/rush-lib/src/api/Subspace.ts b/libraries/rush-lib/src/api/Subspace.ts
index 624b1a33bd6..1058788727e 100644
--- a/libraries/rush-lib/src/api/Subspace.ts
+++ b/libraries/rush-lib/src/api/Subspace.ts
@@ -478,7 +478,6 @@ export class Subspace {
         name,
         bin,
         dependencies,
-        devDependencies,
         peerDependencies,
         optionalDependencies,
         dependenciesMeta,
@@ -500,7 +499,6 @@ export class Subspace {
         name,
         bin,
         dependencies,
-        devDependencies,
         peerDependencies,
         optionalDependencies,
         dependenciesMeta,
diff --git a/libraries/rush-lib/src/api/test/Subspace.test.ts b/libraries/rush-lib/src/api/test/Subspace.test.ts
index b7e01689519..7f1844be7ce 100644
--- a/libraries/rush-lib/src/api/test/Subspace.test.ts
+++ b/libraries/rush-lib/src/api/test/Subspace.test.ts
@@ -74,4 +74,80 @@ describe(Subspace.name, () => {
       expect(hashWithCatalogs).toBeDefined();
     });
   });
+
+  describe('getPackageJsonInjectedDependenciesHash', () => {
+    it('returns undefined when no injected dependencies exist', () => {
+      const rushJsonFilename: string = path.resolve(__dirname, 'repo', 'rush-pnpm.json');
+      const rushConfiguration: RushConfiguration =
+        RushConfiguration.loadFromConfigurationFile(rushJsonFilename);
+      const defaultSubspace: Subspace = rushConfiguration.defaultSubspace;
+
+      const hash: string | undefined = defaultSubspace.getPackageJsonInjectedDependenciesHash();
+      expect(hash).toBeUndefined();
+    });
+
+    it('computes a hash when injected dependencies exist', () => {
+      const rushJsonFilename: string = path.resolve(__dirname, 'repoInjectedDeps', 'rush.json');
+      const rushConfiguration: RushConfiguration =
+        RushConfiguration.loadFromConfigurationFile(rushJsonFilename);
+      const defaultSubspace: Subspace = rushConfiguration.defaultSubspace;
+
+      const hash: string | undefined = defaultSubspace.getPackageJsonInjectedDependenciesHash();
+      expect(hash).toBeDefined();
+      expect(typeof hash).toBe('string');
+      expect(hash).toHaveLength(40); // SHA1 hash
+    });
+
+    it('does not change when devDependencies of the injected package change', () => {
+      const rushJsonFilename: string = path.resolve(__dirname, 'repoInjectedDeps', 'rush.json');
+      const rushConfiguration: RushConfiguration =
+        RushConfiguration.loadFromConfigurationFile(rushJsonFilename);
+      const defaultSubspace: Subspace = rushConfiguration.defaultSubspace;
+
+      const hashBefore: string | undefined = defaultSubspace.getPackageJsonInjectedDependenciesHash();
+
+      // Mutate devDependencies of the injected provider package
+      const providerProject = rushConfiguration.getProjectByName('provider')!;
+      const originalDevDeps = providerProject.packageJson.devDependencies;
+      providerProject.packageJson.devDependencies = {
+        ...originalDevDeps,
+        jest: '^29.0.0'
+      };
+
+      const hashAfter: string | undefined = defaultSubspace.getPackageJsonInjectedDependenciesHash();
+
+      expect(hashBefore).toBeDefined();
+      expect(hashAfter).toBeDefined();
+      expect(hashBefore).toBe(hashAfter);
+
+      // Restore
+      providerProject.packageJson.devDependencies = originalDevDeps;
+    });
+
+    it('changes when production dependencies of the injected package change', () => {
+      const rushJsonFilename: string = path.resolve(__dirname, 'repoInjectedDeps', 'rush.json');
+      const rushConfiguration: RushConfiguration =
+        RushConfiguration.loadFromConfigurationFile(rushJsonFilename);
+      const defaultSubspace: Subspace = rushConfiguration.defaultSubspace;
+
+      const hashBefore: string | undefined = defaultSubspace.getPackageJsonInjectedDependenciesHash();
+
+      // Mutate dependencies of the injected provider package
+      const providerProject = rushConfiguration.getProjectByName('provider')!;
+      const originalDeps = providerProject.packageJson.dependencies;
+      providerProject.packageJson.dependencies = {
+        ...originalDeps,
+        axios: '^1.6.0'
+      };
+
+      const hashAfter: string | undefined = defaultSubspace.getPackageJsonInjectedDependenciesHash();
+
+      expect(hashBefore).toBeDefined();
+      expect(hashAfter).toBeDefined();
+      expect(hashBefore).not.toBe(hashAfter);
+
+      // Restore
+      providerProject.packageJson.dependencies = originalDeps;
+    });
+  });
 });
diff --git a/libraries/rush-lib/src/api/test/repoInjectedDeps/consumer/package.json b/libraries/rush-lib/src/api/test/repoInjectedDeps/consumer/package.json
new file mode 100644
index 00000000000..9fb49f623fd
--- /dev/null
+++ b/libraries/rush-lib/src/api/test/repoInjectedDeps/consumer/package.json
@@ -0,0 +1,12 @@
+{
+  "name": "consumer",
+  "version": "1.0.0",
+  "dependencies": {
+    "provider": "workspace:*"
+  },
+  "dependenciesMeta": {
+    "provider": {
+      "injected": true
+    }
+  }
+}
diff --git a/libraries/rush-lib/src/api/test/repoInjectedDeps/provider/package.json b/libraries/rush-lib/src/api/test/repoInjectedDeps/provider/package.json
new file mode 100644
index 00000000000..22b969cb820
--- /dev/null
+++ b/libraries/rush-lib/src/api/test/repoInjectedDeps/provider/package.json
@@ -0,0 +1,10 @@
+{
+  "name": "provider",
+  "version": "1.0.0",
+  "dependencies": {
+    "lodash": "^4.17.21"
+  },
+  "devDependencies": {
+    "typescript": "~5.3.0"
+  }
+}
diff --git a/libraries/rush-lib/src/api/test/repoInjectedDeps/rush.json b/libraries/rush-lib/src/api/test/repoInjectedDeps/rush.json
new file mode 100644
index 00000000000..eebb706445e
--- /dev/null
+++ b/libraries/rush-lib/src/api/test/repoInjectedDeps/rush.json
@@ -0,0 +1,17 @@
+{
+  "pnpmVersion": "9.5.0",
+  "rushVersion": "5.46.1",
+  "projectFolderMinDepth": 1,
+  "projectFolderMaxDepth": 99,
+
+  "projects": [
+    {
+      "packageName": "consumer",
+      "projectFolder": "consumer"
+    },
+    {
+      "packageName": "provider",
+      "projectFolder": "provider"
+    }
+  ]
+}