diff --git a/core/http/react-ui/src/pages/AgentChat.jsx b/core/http/react-ui/src/pages/AgentChat.jsx
index eb19e1e6a4fb..ae4f5c83bf53 100644
--- a/core/http/react-ui/src/pages/AgentChat.jsx
+++ b/core/http/react-ui/src/pages/AgentChat.jsx
@@ -139,7 +139,8 @@ export default function AgentChat() {
           id: nextId(),
           sender,
           content: data.content || data.message || '',
-          timestamp: data.timestamp ? Math.floor(data.timestamp / 1e6) : Date.now(),
+          // Backend sends Unix milliseconds (see core/services/agents events).
+          timestamp: data.timestamp || Date.now(),
         }
         if (data.metadata && Object.keys(data.metadata).length > 0) {
           msg.metadata = data.metadata
diff --git a/core/services/agents/events.go b/core/services/agents/events.go
index 9a214acf6f05..b187b295ad25 100644
--- a/core/services/agents/events.go
+++ b/core/services/agents/events.go
@@ -27,7 +27,7 @@ type AgentEvent struct {
 	Content        string `json:"content,omitempty"`
 	MessageID      string `json:"message_id,omitempty"`
 	Metadata       string `json:"metadata,omitempty"` // JSON metadata
-	Timestamp      int64  `json:"timestamp"`
+	Timestamp      int64  `json:"timestamp"`                 // Unix milliseconds (set by PublishEvent)
 }
 
 // AgentCancelEvent is the NATS message payload for cancelling agent execution.
@@ -61,8 +61,14 @@ func NewEventBridge(nc messaging.MessagingClient, store *AgentStore, instanceID
 }
 
 // PublishEvent publishes an agent event to NATS for SSE bridging.
+//
+// Timestamp is emitted in Unix milliseconds to match the local dispatcher's
+// json_message events (see dispatcher.go) and the React UI, which feeds the
+// value straight into `new Date(ts)`. Milliseconds also stay within JS's
+// safe-integer range, whereas nanoseconds (~1.7e18) do not and lose precision
+// when parsed as a JSON number.
 func (b *EventBridge) PublishEvent(agentName, userID string, evt AgentEvent) error {
-	evt.Timestamp = time.Now().UnixNano()
+	evt.Timestamp = time.Now().UnixMilli()
 	subject := messaging.SubjectAgentEvents(agentName, userID)
 	return b.nats.Publish(subject, evt)
 }
diff --git a/core/services/agents/events_test.go b/core/services/agents/events_test.go
new file mode 100644
index 000000000000..f103f7982e57
--- /dev/null
+++ b/core/services/agents/events_test.go
@@ -0,0 +1,78 @@
+package agents
+
+import (
+	"time"
+
+	"github.com/mudler/LocalAI/core/services/messaging"
+
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+)
+
+// fakeMessagingClient implements messaging.MessagingClient and captures the
+// last published payload so tests can assert on it.
+type fakeMessagingClient struct {
+	lastSubject string
+	lastData    any
+}
+
+func (f *fakeMessagingClient) Publish(subject string, data any) error {
+	f.lastSubject = subject
+	f.lastData = data
+	return nil
+}
+
+func (f *fakeMessagingClient) Subscribe(string, func([]byte)) (messaging.Subscription, error) {
+	return &fakeSub{}, nil
+}
+
+func (f *fakeMessagingClient) QueueSubscribe(string, string, func([]byte)) (messaging.Subscription, error) {
+	return &fakeSub{}, nil
+}
+
+func (f *fakeMessagingClient) QueueSubscribeReply(string, string, func([]byte, func([]byte))) (messaging.Subscription, error) {
+	return &fakeSub{}, nil
+}
+
+func (f *fakeMessagingClient) SubscribeReply(string, func([]byte, func([]byte))) (messaging.Subscription, error) {
+	return &fakeSub{}, nil
+}
+
+func (f *fakeMessagingClient) Request(string, []byte, time.Duration) ([]byte, error) {
+	return nil, nil
+}
+
+func (f *fakeMessagingClient) IsConnected() bool { return true }
+func (f *fakeMessagingClient) Close()            {}
+
+type fakeSub struct{}
+
+func (s *fakeSub) Unsubscribe() error { return nil }
+
+var _ = Describe("EventBridge", func() {
+	Describe("PublishEvent timestamp", func() {
+		// Regression for #9867: agent chat messages rendered a broken
+		// timestamp ("Invalid Timestamp" / "12:00 AM") in the web UI because
+		// this path emitted Unix nanoseconds while the local dispatcher and the
+		// React UI both expect Unix milliseconds. Nanoseconds also overflow JS's
+		// safe-integer range. The timestamp must be in milliseconds.
+		It("emits the timestamp in Unix milliseconds", func() {
+			fake := &fakeMessagingClient{}
+			bridge := NewEventBridge(fake, nil, "instance-1")
+
+			before := time.Now().UnixMilli()
+			err := bridge.PublishMessage("agent", "user", "agent", "hello", "msg-1")
+			after := time.Now().UnixMilli()
+
+			Expect(err).ToNot(HaveOccurred())
+
+			evt, ok := fake.lastData.(AgentEvent)
+			Expect(ok).To(BeTrue(), "published payload should be an AgentEvent")
+
+			// A millisecond timestamp falls within [before, after]; a nanosecond
+			// one (~1e6 larger) would be far outside this window.
+			Expect(evt.Timestamp).To(BeNumerically(">=", before))
+			Expect(evt.Timestamp).To(BeNumerically("<=", after))
+		})
+	})
+})