diff --git a/.github/workflows/run-script.yml b/.github/workflows/run-script.yml
index 5ece980..1f3e4af 100644
--- a/.github/workflows/run-script.yml
+++ b/.github/workflows/run-script.yml
@@ -11,10 +11,10 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
-      - name: Setup .NET 8.0
+      - name: Setup .NET 9.0
         uses: actions/setup-dotnet@v4
         with:
-          dotnet-version: '8.0'
+          dotnet-version: '9.0'
 
       - name: Run script
         shell: pwsh
diff --git a/Runner/Helpers/GitHelper.cs b/Runner/Helpers/GitHelper.cs
index 94b0843..3eff0f8 100644
--- a/Runner/Helpers/GitHelper.cs
+++ b/Runner/Helpers/GitHelper.cs
@@ -30,4 +30,19 @@ private static bool ShouldSkipLine(string line)
             span.StartsWith("@@", StringComparison.Ordinal) ||
             span.StartsWith("\\ No newline at end of file", StringComparison.Ordinal);
     }
+
+    public static async Task<List<string>> GetChangedFilesAsync(JobBase job, string baselineRef, string workDir)
+    {
+        List<string> lines = [];
+
+        await job.RunProcessAsync("git",
+            $"diff --name-only {baselineRef}",
+            lines,
+            workDir: workDir,
+            checkExitCode: false,
+            suppressOutputLogs: true,
+            suppressStartingLog: true);
+
+        return lines;
+    }
 }
diff --git a/Runner/Jobs/JitDiffJob.cs b/Runner/Jobs/JitDiffJob.cs
index dc151c0..88875dc 100644
--- a/Runner/Jobs/JitDiffJob.cs
+++ b/Runner/Jobs/JitDiffJob.cs
@@ -80,7 +80,9 @@ public static async Task BuildAndCopyRuntimeBranchBitsAsync(JobBase job, string
     {
         string arch = IsArm ? "arm64" : "x64";
 
-        await job.RunProcessAsync("bash", $"build.sh clr+libs -c Release {RuntimeHelpers.LibrariesExtraBuildArgs}", logPrefix: $"{branch} release", workDir: "runtime");
+        string targets = await ShouldBuildsLibsAsync() ? "clr+libs" : "clr";
+
+        await job.RunProcessAsync("bash", $"build.sh {targets} -c Release {RuntimeHelpers.LibrariesExtraBuildArgs}", logPrefix: $"{branch} release", workDir: "runtime");
 
         Task copyReleaseBitsTask = RuntimeHelpers.CopyReleaseArtifactsAsync(job, branch, $"artifacts-{branch}");
 
@@ -94,6 +96,20 @@ public static async Task BuildAndCopyRuntimeBranchBitsAsync(JobBase job, string
         }
 
         await copyReleaseBitsTask;
+
+        async Task<bool> ShouldBuildsLibsAsync()
+        {
+            if (branch == "pr")
+            {
+                List<string> changedFiles = await GitHelper.GetChangedFilesAsync(job, "main", "runtime");
+
+                return changedFiles.Any(f =>
+                    !f.StartsWith("src/coreclr/", StringComparison.OrdinalIgnoreCase) ||
+                    f.Contains("/System.Private.CoreLib/", StringComparison.OrdinalIgnoreCase));
+            }
+
+            return true;
+        }
     }
 
     private async Task<string> CollectFrameworksDiffsAsync()
diff --git a/Runner/Runner.csproj b/Runner/Runner.csproj
index f38bcc4..fdd2b42 100644
--- a/Runner/Runner.csproj
+++ b/Runner/Runner.csproj
@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>net8.0</TargetFramework>
+    <TargetFramework>net9.0</TargetFramework>
     <Nullable>enable</Nullable>
     <NoWarn>${NoWarn};IDE0305</NoWarn>
   </PropertyGroup>