diff --git a/compute_tools/src/compute.rs b/compute_tools/src/compute.rs
index dca6becd39..da5ad00da6 100644
--- a/compute_tools/src/compute.rs
+++ b/compute_tools/src/compute.rs
@@ -67,8 +67,9 @@ pub struct ComputeNode {
 pub struct ComputeState {
     pub start_time: DateTime<Utc>,
     pub status: ComputeStatus,
-    /// Timestamp of the last Postgres activity
-    pub last_active: DateTime<Utc>,
+    /// Timestamp of the last Postgres activity. It could be `None` if
+    /// compute wasn't used since start.
+    pub last_active: Option<DateTime<Utc>>,
     pub error: Option<String>,
     pub pspec: Option<ParsedSpec>,
     pub metrics: ComputeMetrics,
@@ -79,7 +80,7 @@ impl ComputeState {
         Self {
             start_time: Utc::now(),
             status: ComputeStatus::Empty,
-            last_active: Utc::now(),
+            last_active: None,
             error: None,
             pspec: None,
             metrics: ComputeMetrics::default(),
diff --git a/compute_tools/src/http/openapi_spec.yaml b/compute_tools/src/http/openapi_spec.yaml
index cc8f074a50..2680269756 100644
--- a/compute_tools/src/http/openapi_spec.yaml
+++ b/compute_tools/src/http/openapi_spec.yaml
@@ -181,8 +181,8 @@ components:
     ComputeState:
       type: object
       required:
+        - start_time
         - status
-        - last_active
       properties:
         start_time:
           type: string
@@ -195,11 +195,13 @@ components:
           $ref: '#/components/schemas/ComputeStatus'
         last_active:
           type: string
-          description: The last detected compute activity timestamp in UTC and RFC3339 format.
+          description: |
+            The last detected compute activity timestamp in UTC and RFC3339 format.
+            It could be empty if compute was never used by user since start.
           example: "2022-10-12T07:20:50.52Z"
         error:
           type: string
-          description: Text of the error during compute startup, if any.
+          description: Text of the error during compute startup or reconfiguration, if any.
           example: ""
         tenant:
           type: string
@@ -222,9 +224,12 @@ components:
     ComputeStatus:
       type: string
       enum:
+        - empty
         - init
         - failed
         - running
+        - configuration_pending
+        - configuration
       example: running
 
     #
diff --git a/compute_tools/src/monitor.rs b/compute_tools/src/monitor.rs
index a30b52aed4..d2e7b698dd 100644
--- a/compute_tools/src/monitor.rs
+++ b/compute_tools/src/monitor.rs
@@ -74,7 +74,7 @@ fn watch_compute_activity(compute: &ComputeNode) {
                             // Found non-idle backend, so the last activity is NOW.
                             // Save it and exit the for loop. Also clear the idle backend
                             // `state_change` timestamps array as it doesn't matter now.
-                            last_active = Utc::now();
+                            last_active = Some(Utc::now());
                             idle_backs.clear();
                             break;
                         }
@@ -82,15 +82,16 @@ fn watch_compute_activity(compute: &ComputeNode) {
 
                     // Get idle backend `state_change` with the max timestamp.
                     if let Some(last) = idle_backs.iter().max() {
-                        last_active = *last;
+                        last_active = Some(*last);
                     }
                 }
 
                 // Update the last activity in the shared state if we got a more recent one.
                 let mut state = compute.state.lock().unwrap();
+                // NB: `Some(<DateTime>)` is always greater than `None`.
                 if last_active > state.last_active {
                     state.last_active = last_active;
-                    debug!("set the last compute activity time to: {}", last_active);
+                    debug!("set the last compute activity time to: {:?}", last_active);
                 }
             }
             Err(e) => {
diff --git a/libs/compute_api/src/responses.rs b/libs/compute_api/src/responses.rs
index c409563b56..d181c018b1 100644
--- a/libs/compute_api/src/responses.rs
+++ b/libs/compute_api/src/responses.rs
@@ -19,7 +19,7 @@ pub struct ComputeStatusResponse {
     pub timeline: Option<String>,
     pub status: ComputeStatus,
     #[serde(serialize_with = "rfc3339_serialize")]
-    pub last_active: DateTime<Utc>,
+    pub last_active: Option<DateTime<Utc>>,
     pub error: Option<String>,
 }
 
@@ -29,7 +29,7 @@ pub struct ComputeState {
     pub status: ComputeStatus,
     /// Timestamp of the last Postgres activity
     #[serde(serialize_with = "rfc3339_serialize")]
-    pub last_active: DateTime<Utc>,
+    pub last_active: Option<DateTime<Utc>>,
     pub error: Option<String>,
 }
 
@@ -54,11 +54,15 @@ pub enum ComputeStatus {
     Failed,
 }
 
-fn rfc3339_serialize<S>(x: &DateTime<Utc>, s: S) -> Result<S::Ok, S::Error>
+fn rfc3339_serialize<S>(x: &Option<DateTime<Utc>>, s: S) -> Result<S::Ok, S::Error>
 where
     S: Serializer,
 {
-    x.to_rfc3339().serialize(s)
+    if let Some(x) = x {
+        x.to_rfc3339().serialize(s)
+    } else {
+        s.serialize_none()
+    }
 }
 
 /// Response of the /metrics.json API