diff --git a/jenkins/L0_MergeRequest.groovy b/jenkins/L0_MergeRequest.groovy
index 1ef2aac37c97..6329397a58f3 100644
--- a/jenkins/L0_MergeRequest.groovy
+++ b/jenkins/L0_MergeRequest.groovy
@@ -749,7 +749,7 @@ def getGithubMRChangedFile(pipeline, githubPrApiUrl, function, filePath="") {
                 }
                 rawDataList.find { rawData ->
                     if (rawData.get("filename") == filePath || rawData.get("previous_filename") == filePath) {
-                        result = rawData.get("patch")
+                        result = rawData.get("patch") ?: ""
                         return true
                     }
                     return false
@@ -769,7 +769,7 @@ def getGithubMRChangedFile(pipeline, githubPrApiUrl, function, filePath="") {
                 rawDataList.each { rawData ->
                     [rawData.get("filename"), rawData.get("previous_filename")]
                         .findAll { it }
-                        .each { changedFilePath -> result[changedFilePath] = rawData.get("patch") }
+                        .each { changedFilePath -> result[changedFilePath] = rawData.get("patch") ?: "" }
                 }
             }
             if (!rawDataList) { break }
@@ -778,6 +778,90 @@ def getGithubMRChangedFile(pipeline, githubPrApiUrl, function, filePath="") {
     return result
 }
 
+def getGitMirrorMRChangedFile(pipeline, globalVars, function, filePath="", filePaths=[]) {
+    def wrapperBuildNumber = globalVars[ACTION_INFO]?.get("parents")?.getAt(0)?.get("build_number")?.toString()
+    def headCommit = env.gitlabCommit?.toString()
+    def baseRef = "refs/heads/prjob/${wrapperBuildNumber}/base"
+    pipeline.withEnv(["GIT_DIFF_BASE_REF=${baseRef}"]) {
+        withCredentials([gitUsernamePassword(credentialsId: 'svc_tensorrt_gitlab_api_token', gitToolName: 'Default'),]) {
+            pipeline.sh "git -C ${LLM_ROOT} fetch --no-tags --depth=1 origin \"\${GIT_DIFF_BASE_REF}\""
+        }
+    }
+    def baseCommit = pipeline.sh(script: "git -C ${LLM_ROOT} rev-parse FETCH_HEAD", returnStdout: true).trim()
+    pipeline.echo("Using internal Git mirror diff: ${baseCommit}...${headCommit}")
+
+    def nameStatus = pipeline.sh(
+        script: "git -C ${LLM_ROOT} -c core.quotepath=false diff --name-status --find-renames ${baseCommit} ${headCommit}",
+        returnStdout: true
+    )
+    def changedFiles = nameStatus.readLines().collect { line ->
+        def fields = line.split('\t', -1)
+        def paths = []
+        for (int index = 1; index < fields.length; index++) {
+            if (fields[index]) {
+                paths.add(fields[index])
+            }
+        }
+        [status: fields[0], paths: paths]
+    }
+    if (function == "getChangedFileList") {
+        return changedFiles.collectMany { changedFile ->
+            changedFile.status.startsWith("R") || changedFile.status.startsWith("C")? changedFile.paths.reverse(): changedFile.paths
+        }
+    }
+
+    def renamePaths = [:]
+    changedFiles.findAll { changedFile ->
+        changedFile.status.startsWith("R") || changedFile.status.startsWith("C")
+    }.each { changedFile ->
+        changedFile.paths.each { changedFilePath -> renamePaths[changedFilePath] = changedFile.paths }
+    }
+    def cachedDiffs = [:]
+    def getFileDiff = { changedFilePath ->
+        if (cachedDiffs.containsKey(changedFilePath)) {
+            return cachedDiffs[changedFilePath]
+        }
+        def diffPaths = renamePaths.get(changedFilePath, [changedFilePath])
+        def rawDiff = ""
+        pipeline.withEnv([
+            "GIT_DIFF_PATH=${diffPaths[0]}",
+            "GIT_DIFF_RENAME_PATH=${diffPaths.size() > 1 ? diffPaths[1] : diffPaths[0]}",
+        ]) {
+            rawDiff = pipeline.sh(
+                script: "git -C ${LLM_ROOT} diff --unified=3 --inter-hunk-context=1 --find-renames ${baseCommit} ${headCommit} -- \":(literal)\${GIT_DIFF_PATH}\" \":(literal)\${GIT_DIFF_RENAME_PATH}\"",
+                returnStdout: true
+            )
+        }
+        def lines = rawDiff.readLines()
+        def firstHunk = lines.findIndexOf { it.startsWith("@@") }
+        def diff = firstHunk < 0 ? "" : lines.drop(firstHunk).join("\n")
+        diffPaths.each { diffPath -> cachedDiffs[diffPath] = diff }
+        return diff
+    }
+
+    if (function == "getOneFileChanges") {
+        return getFileDiff(filePath)
+    }
+    if (function == "getFileChanges") {
+        return filePaths.unique().collectEntries { changedFilePath -> [(changedFilePath): getFileDiff(changedFilePath)] }
+    }
+    pipeline.error("Unsupported PR diff operation: ${function}")
+}
+
+def getGithubMRChangedFileWithFallback(pipeline, globalVars, function, filePath="", filePaths=[]) {
+    try {
+        return getGithubMRChangedFile(pipeline, globalVars[GITHUB_PR_API_URL], function, filePath)
+    } catch (InterruptedException e) {
+        throw e
+    } catch (Exception e) {
+        pipeline.echo("WARNING: [PR_DIFF_FALLBACK] GitHub PR files API failed for ${function}; " +
+                      "trying the internal Git mirror. Error: ${e.toString()}")
+        def result = getGitMirrorMRChangedFile(pipeline, globalVars, function, filePath, filePaths)
+        pipeline.echo("WARNING: [PR_DIFF_FALLBACK] Internal Git mirror fallback succeeded for ${function}.")
+        return result
+    }
+}
+
 // Gate multi-GPU stages behind 'ci: full pre-merge approved' label.
 // Uses trtllm_utils.validatePRLabelApproval() from the shared lib to verify
 // both label existence and that the labeler is an active team member.
@@ -843,7 +927,7 @@ def getMergeRequestChangedFileList(pipeline, globalVars) {
     try {
         def changedFileList = []
         if (githubPrApiUrl != null) {
-            changedFileList = getGithubMRChangedFile(pipeline, githubPrApiUrl, "getChangedFileList")
+            changedFileList = getGithubMRChangedFileWithFallback(pipeline, globalVars, "getChangedFileList")
         } else {
             changedFileList = getGitlabMRChangedFile(pipeline, "getChangedFileList")
         }
@@ -876,7 +960,7 @@ def getMergeRequestOneFileChanges(pipeline, globalVars, filePath) {
     def diff = ""
 
     if (githubPrApiUrl != null) {
-        diff = getGithubMRChangedFile(pipeline, githubPrApiUrl, "getOneFileChanges", filePath)
+        diff = getGithubMRChangedFileWithFallback(pipeline, globalVars, "getOneFileChanges", filePath)
     } else {
         diff = getGitlabMRChangedFile(pipeline, "getOneFileChanges", filePath)
     }
@@ -977,7 +1061,7 @@ def getCbtsResult(pipeline, testFilter, globalVars)
         if (filesNeedingDiff) {
             def githubPrApiUrl = globalVars[GITHUB_PR_API_URL]
             def fileChanges = githubPrApiUrl != null
-                ? getGithubMRChangedFile(pipeline, githubPrApiUrl, "getFileChanges")
+                ? getGithubMRChangedFileWithFallback(pipeline, globalVars, "getFileChanges", "", filesNeedingDiff)
                 : getGitlabMRChangedFile(pipeline, "getFileChanges")
             diffs = filesNeedingDiff.collectEntries { filePath ->
                 // Null (patch omitted for binary / rename / too-large diffs) coerces to empty.