diff --git a/crates/common/protos/local/temporal/sdk/core/workflow_activation/workflow_activation.proto b/crates/common/protos/local/temporal/sdk/core/workflow_activation/workflow_activation.proto
index fb8d90756..7eaa1ac77 100644
--- a/crates/common/protos/local/temporal/sdk/core/workflow_activation/workflow_activation.proto
+++ b/crates/common/protos/local/temporal/sdk/core/workflow_activation/workflow_activation.proto
@@ -92,6 +92,8 @@ message WorkflowActivation {
     // build id, if this worker was using the deprecated Build ID-only
     // feature(s).
     common.WorkerDeploymentVersion deployment_version_for_current_task = 9;
+    // The last seen SDK version from the most recent WFT completed event
+    string last_sdk_version = 10;
 }
 
 message WorkflowActivationJob {
diff --git a/crates/common/src/protos/mod.rs b/crates/common/src/protos/mod.rs
index 49545ed3d..1121a1f63 100644
--- a/crates/common/src/protos/mod.rs
+++ b/crates/common/src/protos/mod.rs
@@ -519,6 +519,7 @@ pub mod coresdk {
                 history_size_bytes: 0,
                 continue_as_new_suggested: false,
                 deployment_version_for_current_task: None,
+                last_sdk_version: String::new(),
             }
         }
 
diff --git a/crates/sdk-core/src/internal_flags.rs b/crates/sdk-core/src/internal_flags.rs
index 958e6459e..2d885ab2c 100644
--- a/crates/sdk-core/src/internal_flags.rs
+++ b/crates/sdk-core/src/internal_flags.rs
@@ -203,6 +203,15 @@ impl InternalFlags {
             Self::Disabled => Either::Right(iter::empty()),
         }
     }
+
+    pub(crate) fn last_sdk_version(&self) -> Option<&str> {
+        match self {
+            InternalFlags::Enabled {
+                last_sdk_version, ..
+            } if !last_sdk_version.is_empty() => Some(last_sdk_version),
+            InternalFlags::Enabled { .. } | InternalFlags::Disabled => None,
+        }
+    }
 }
 
 impl CoreInternalFlags {
diff --git a/crates/sdk-core/src/worker/workflow/machines/workflow_machines.rs b/crates/sdk-core/src/worker/workflow/machines/workflow_machines.rs
index 834b828bc..23411f008 100644
--- a/crates/sdk-core/src/worker/workflow/machines/workflow_machines.rs
+++ b/crates/sdk-core/src/worker/workflow/machines/workflow_machines.rs
@@ -465,6 +465,11 @@ impl WorkflowMachines {
             continue_as_new_suggested: self.continue_as_new_suggested,
             deployment_version_for_current_task: deployment_version_for_current_task
                 .map(Into::into),
+            last_sdk_version: (*self.observed_internal_flags)
+                .borrow()
+                .last_sdk_version()
+                .unwrap_or_default()
+                .to_owned(),
         }
     }