diff --git a/src/NATS.Server/JetStream/Consumers/DeliveryInterestTracker.cs b/src/NATS.Server/JetStream/Consumers/DeliveryInterestTracker.cs
new file mode 100644
index 0000000..870130e
--- /dev/null
+++ b/src/NATS.Server/JetStream/Consumers/DeliveryInterestTracker.cs
@@ -0,0 +1,65 @@
+namespace NATS.Server.JetStream.Consumers;
+
+/// <summary>
+/// Tracks whether there are active subscribers on a consumer's delivery subject.
+/// When interest drops to zero and remains absent for a configurable timeout, the
+/// consumer can be cleaned up (for ephemeral consumers) or paused (for durable ones).
+/// Go reference: consumer.go hasDeliveryInterest, deleteNotActive.
+/// </summary>
+public sealed class DeliveryInterestTracker
+{
+    private readonly TimeSpan _inactiveTimeout;
+    private int _subscriberCount;
+    private DateTime? _lastUnsubscribeUtc;
+
+    public DeliveryInterestTracker(TimeSpan? inactiveTimeout = null)
+    {
+        _inactiveTimeout = inactiveTimeout ?? TimeSpan.FromSeconds(30);
+    }
+
+    /// <summary>True when at least one subscriber exists on the delivery subject.</summary>
+    public bool HasInterest => Volatile.Read(ref _subscriberCount) > 0;
+
+    /// <summary>Current subscriber count.</summary>
+    public int SubscriberCount => Volatile.Read(ref _subscriberCount);
+
+    /// <summary>
+    /// True when interest has been absent for longer than the inactive timeout.
+    /// Used by ephemeral consumers to trigger auto-deletion.
+    /// Go reference: consumer.go deleteNotActive.
+    /// </summary>
+    public bool ShouldDelete
+    {
+        get
+        {
+            if (HasInterest) return false;
+            if (_lastUnsubscribeUtc == null) return false;
+            return DateTime.UtcNow - _lastUnsubscribeUtc.Value >= _inactiveTimeout;
+        }
+    }
+
+    /// <summary>Records a new subscriber on the delivery subject.</summary>
+    public void OnSubscribe()
+    {
+        Interlocked.Increment(ref _subscriberCount);
+        _lastUnsubscribeUtc = null; // Reset the inactivity timer
+    }
+
+    /// <summary>Records removal of a subscriber from the delivery subject.</summary>
+    public void OnUnsubscribe()
+    {
+        var count = Interlocked.Decrement(ref _subscriberCount);
+        if (count <= 0)
+        {
+            Interlocked.Exchange(ref _subscriberCount, 0); // floor at 0
+            _lastUnsubscribeUtc = DateTime.UtcNow;
+        }
+    }
+
+    /// <summary>Resets the tracker to initial state.</summary>
+    public void Reset()
+    {
+        Interlocked.Exchange(ref _subscriberCount, 0);
+        _lastUnsubscribeUtc = null;
+    }
+}
diff --git a/tests/NATS.Server.Tests/JetStream/Consumers/DeliveryInterestTests.cs b/tests/NATS.Server.Tests/JetStream/Consumers/DeliveryInterestTests.cs
new file mode 100644
index 0000000..2742ea5
--- /dev/null
+++ b/tests/NATS.Server.Tests/JetStream/Consumers/DeliveryInterestTests.cs
@@ -0,0 +1,207 @@
+// Go: consumer.go hasDeliveryInterest, deleteNotActive
+using NATS.Server.JetStream.Consumers;
+
+namespace NATS.Server.Tests.JetStream.Consumers;
+
+public class DeliveryInterestTests
+{
+    // -------------------------------------------------------------------------
+    // Test 1 — HasInterest is true after a subscribe
+    //
+    // Go reference: consumer.go hasDeliveryInterest — returns true when at
+    // least one client is subscribed to the push consumer's deliver subject.
+    // -------------------------------------------------------------------------
+    [Fact]
+    public void HasInterest_true_after_subscribe()
+    {
+        var tracker = new DeliveryInterestTracker();
+
+        tracker.OnSubscribe();
+
+        tracker.HasInterest.ShouldBeTrue();
+    }
+
+    // -------------------------------------------------------------------------
+    // Test 2 — HasInterest is false initially (no subscribers)
+    //
+    // Go reference: consumer.go — on creation there are no delivery subscribers.
+    // -------------------------------------------------------------------------
+    [Fact]
+    public void HasInterest_false_initially()
+    {
+        var tracker = new DeliveryInterestTracker();
+
+        tracker.HasInterest.ShouldBeFalse();
+    }
+
+    // -------------------------------------------------------------------------
+    // Test 3 — HasInterest drops to false after all subscribers unsubscribe
+    //
+    // Go reference: consumer.go hasDeliveryInterest — once subscription count
+    // reaches 0, interest is gone.
+    // -------------------------------------------------------------------------
+    [Fact]
+    public void HasInterest_false_after_all_unsubscribe()
+    {
+        var tracker = new DeliveryInterestTracker();
+
+        tracker.OnSubscribe();
+        tracker.OnSubscribe();
+        tracker.OnUnsubscribe();
+        tracker.OnUnsubscribe();
+
+        tracker.HasInterest.ShouldBeFalse();
+    }
+
+    // -------------------------------------------------------------------------
+    // Test 4 — SubscriberCount tracks multiple subscribers accurately
+    //
+    // Go reference: consumer.go — the interest count must reflect the exact
+    // number of active push-consumer delivery subscriptions.
+    // -------------------------------------------------------------------------
+    [Fact]
+    public void SubscriberCount_tracks_multiple_subscribers()
+    {
+        var tracker = new DeliveryInterestTracker();
+
+        tracker.SubscriberCount.ShouldBe(0);
+
+        tracker.OnSubscribe();
+        tracker.SubscriberCount.ShouldBe(1);
+
+        tracker.OnSubscribe();
+        tracker.SubscriberCount.ShouldBe(2);
+
+        tracker.OnSubscribe();
+        tracker.SubscriberCount.ShouldBe(3);
+
+        tracker.OnUnsubscribe();
+        tracker.SubscriberCount.ShouldBe(2);
+    }
+
+    // -------------------------------------------------------------------------
+    // Test 5 — OnUnsubscribe floors subscriber count at zero (no negatives)
+    //
+    // Go reference: consumer.go deleteNotActive — stray unsub events must not
+    // drive the count below zero and corrupt subsequent interest checks.
+    // -------------------------------------------------------------------------
+    [Fact]
+    public void OnUnsubscribe_floors_at_zero()
+    {
+        var tracker = new DeliveryInterestTracker();
+
+        tracker.OnUnsubscribe();
+        tracker.OnUnsubscribe();
+
+        tracker.SubscriberCount.ShouldBe(0);
+        tracker.HasInterest.ShouldBeFalse();
+    }
+
+    // -------------------------------------------------------------------------
+    // Test 6 — ShouldDelete is false while interest exists
+    //
+    // Go reference: consumer.go deleteNotActive — ephemeral cleanup is only
+    // triggered when there are no active subscribers.
+    // -------------------------------------------------------------------------
+    [Fact]
+    public void ShouldDelete_false_when_has_interest()
+    {
+        var tracker = new DeliveryInterestTracker(inactiveTimeout: TimeSpan.FromMilliseconds(1));
+
+        tracker.OnSubscribe();
+
+        tracker.ShouldDelete.ShouldBeFalse();
+    }
+
+    // -------------------------------------------------------------------------
+    // Test 7 — ShouldDelete is false immediately after unsubscribe (timeout
+    //           has not yet elapsed)
+    //
+    // Go reference: consumer.go deleteNotActive — the inactive timeout must
+    // fully elapse before the consumer is eligible for deletion.
+    // -------------------------------------------------------------------------
+    [Fact]
+    public void ShouldDelete_false_immediately_after_unsubscribe()
+    {
+        var tracker = new DeliveryInterestTracker(inactiveTimeout: TimeSpan.FromSeconds(30));
+
+        tracker.OnSubscribe();
+        tracker.OnUnsubscribe();
+
+        // No wait — timeout has not elapsed yet.
+        tracker.ShouldDelete.ShouldBeFalse();
+    }
+
+    // -------------------------------------------------------------------------
+    // Test 8 — ShouldDelete is true after the inactive timeout elapses with
+    //           zero subscribers
+    //
+    // Go reference: consumer.go deleteNotActive — once the configurable
+    // MaxAckPending / inactive threshold passes, the ephemeral consumer is
+    // scheduled for removal.
+    // -------------------------------------------------------------------------
+    [SlopwatchSuppress("SW004", "Intentional timeout test: ShouldDelete requires real wall-clock elapsed time to observe the inactive threshold firing; no synchronisation primitive can replace this")]
+    [Fact]
+    public async Task ShouldDelete_true_after_timeout()
+    {
+        var tracker = new DeliveryInterestTracker(inactiveTimeout: TimeSpan.FromMilliseconds(50));
+
+        tracker.OnSubscribe();
+        tracker.OnUnsubscribe();
+
+        await Task.Delay(100); // Wait for timeout to elapse.
+
+        tracker.ShouldDelete.ShouldBeTrue();
+    }
+
+    // -------------------------------------------------------------------------
+    // Test 9 — Reset clears all state (count and inactivity timer)
+    //
+    // Go reference: consumer.go — Reset is used to reinitialise tracking when
+    // a consumer is re-attached or recreated.
+    // -------------------------------------------------------------------------
+    [SlopwatchSuppress("SW004", "Intentional timeout test: must let the inactive threshold elapse to confirm Reset clears the inactivity timer; no synchronisation primitive can replace this")]
+    [Fact]
+    public async Task Reset_clears_all_state()
+    {
+        var tracker = new DeliveryInterestTracker(inactiveTimeout: TimeSpan.FromMilliseconds(50));
+
+        tracker.OnSubscribe();
+        tracker.OnSubscribe();
+        tracker.OnUnsubscribe();
+        tracker.OnUnsubscribe();
+        await Task.Delay(100); // Let timeout elapse.
+
+        tracker.Reset();
+
+        tracker.SubscriberCount.ShouldBe(0);
+        tracker.HasInterest.ShouldBeFalse();
+        tracker.ShouldDelete.ShouldBeFalse(); // inactivity timer also cleared
+    }
+
+    // -------------------------------------------------------------------------
+    // Test 10 — Subscribing after an unsubscribe clears the inactivity timer
+    //            so ShouldDelete stays false even after the original timeout
+    //
+    // Go reference: consumer.go hasDeliveryInterest — a re-subscription resets
+    // the inactive-since timestamp, preventing spurious cleanup.
+    // -------------------------------------------------------------------------
+    [SlopwatchSuppress("SW004", "Intentional timeout test: must let the original inactive window pass after re-subscribe to confirm the inactivity timer was cleared; no synchronisation primitive can replace this")]
+    [Fact]
+    public async Task Subscribe_clears_inactivity_timer()
+    {
+        var tracker = new DeliveryInterestTracker(inactiveTimeout: TimeSpan.FromMilliseconds(50));
+
+        tracker.OnSubscribe();
+        tracker.OnUnsubscribe();
+
+        // Re-subscribe before the timeout elapses.
+        tracker.OnSubscribe();
+
+        await Task.Delay(100); // Original timeout window passes.
+
+        // Still has interest and timer was reset, so ShouldDelete must be false.
+        tracker.HasInterest.ShouldBeTrue();
+        tracker.ShouldDelete.ShouldBeFalse();
+    }
+}