diff --git a/src/Agent.Sdk/Knob/AgentKnobs.cs b/src/Agent.Sdk/Knob/AgentKnobs.cs
index de5f3894b0..224370922b 100644
--- a/src/Agent.Sdk/Knob/AgentKnobs.cs
+++ b/src/Agent.Sdk/Knob/AgentKnobs.cs
@@ -499,7 +499,13 @@ public class AgentKnobs
             new EnvironmentKnobSource("AZP_AGENT_CLEANUP_PSMODULES_IN_POWERSHELL"),
             new BuiltInDefaultKnobSource("false"));
 
-        public static readonly Knob IgnoreVSTSTaskLib = new Knob(
+        public static readonly Knob DisableCleanRepoDefaultValue = new DeprecatedKnob(
+            nameof(DisableCleanRepoDefaultValue),
+            "Avoid to set default value if build.repository.clean variable is not set on Trigger Yaml UI or in checkout steps yaml config",
+            new EnvironmentKnobSource("AGENT_DISABLE_CLEAN_REPO_DEFAULT_VALUE"),
+            new BuiltInDefaultKnobSource("false"));
+
+          public static readonly Knob IgnoreVSTSTaskLib = new Knob(
             nameof(IgnoreVSTSTaskLib),
             "Ignores the VSTSTaskLib folder when copying tasks.",
             new RuntimeKnobSource("AZP_AGENT_IGNORE_VSTSTASKLIB"),
diff --git a/src/Agent.Worker/Build/BuildJobExtension.cs b/src/Agent.Worker/Build/BuildJobExtension.cs
index de5ac9d9f6..cbc1fcecd1 100644
--- a/src/Agent.Worker/Build/BuildJobExtension.cs
+++ b/src/Agent.Worker/Build/BuildJobExtension.cs
@@ -8,6 +8,7 @@
 using System.IO;
 using System.Linq;
 using Microsoft.TeamFoundation.DistributedTask.Pipelines;
+using Agent.Sdk.Knob;
 
 namespace Microsoft.VisualStudio.Services.Agent.Worker.Build
 {
@@ -257,9 +258,18 @@ private void UpdateCheckoutTasksAndVariables(IExecutionContext executionContext,
                 executionContext.SetVariable(Constants.Variables.Build.RepoGitSubmoduleCheckout, submoduleCheckout.Value.ToString());
             }
 
-            if (repoCleanFromSelf.HasValue)
+            // This condition is for maintaining backward compatibility.
+            // Remove the if-else condition and keep only the context inside the 'else' to set the default value in future releases.
+            if (AgentKnobs.DisableCleanRepoDefaultValue.GetValue(UtilKnobValueContext.Instance()).AsBoolean())
             {
-                executionContext.SetVariable(Constants.Variables.Build.RepoClean, repoCleanFromSelf.Value.ToString());
+                if (repoCleanFromSelf.HasValue)
+                {
+                    executionContext.SetVariable(Constants.Variables.Build.RepoClean, repoCleanFromSelf.Value.ToString());
+                }
+            }
+            else
+            {
+                executionContext.SetVariable(Constants.Variables.Build.RepoClean, repoCleanFromSelf.HasValue ? repoCleanFromSelf.Value.ToString() : "False");
             }
         }