diff --git a/backend/cmd/web/main.go b/backend/cmd/web/main.go
index 4192493..ec2ed56 100644
--- a/backend/cmd/web/main.go
+++ b/backend/cmd/web/main.go
@@ -149,7 +149,7 @@ func main() {
 	fileDeps := web.FilesDeps{Queries: q, Files: filesStore, MaxUploadMB: maxUploadMB}
 	etapeDeps := web.EtapesDeps{Queries: q}
 	eventDeps := web.EventsDeps{Queries: q}
-	discussionDeps := web.DiscussionDeps{Queries: q}
+	discussionDeps := web.DiscussionDeps{Queries: q, Realtime: web.NewDiscussionBroker()}
 	planningDeps := web.PlanningDeps{Queries: q}
 
 	// D-09: pass the embedded static FS — binary has zero runtime file dependencies.
diff --git a/backend/internal/web/discussion_broker.go b/backend/internal/web/discussion_broker.go
new file mode 100644
index 0000000..f2f2680
--- /dev/null
+++ b/backend/internal/web/discussion_broker.go
@@ -0,0 +1,84 @@
+package web
+
+import (
+	"context"
+	"sync"
+
+	"github.com/google/uuid"
+)
+
+type DiscussionEvent struct {
+	TabloID       uuid.UUID `json:"tabloId"`
+	MessageID     uuid.UUID `json:"messageId"`
+	AuthorUserID  uuid.UUID `json:"authorUserId"`
+	MessageHTML   string    `json:"messageHtml"`
+	RefreshUnread bool      `json:"refreshUnread"`
+}
+
+type DiscussionRealtime interface {
+	Subscribe(ctx context.Context, tabloID uuid.UUID) (<-chan DiscussionEvent, func())
+	Publish(event DiscussionEvent)
+}
+
+type DiscussionBroker struct {
+	mu          sync.Mutex
+	nextID      int
+	subscribers map[uuid.UUID]map[int]chan DiscussionEvent
+}
+
+func NewDiscussionBroker() *DiscussionBroker {
+	return &DiscussionBroker{subscribers: make(map[uuid.UUID]map[int]chan DiscussionEvent)}
+}
+
+func (b *DiscussionBroker) Subscribe(ctx context.Context, tabloID uuid.UUID) (<-chan DiscussionEvent, func()) {
+	ch := make(chan DiscussionEvent, 8)
+
+	b.mu.Lock()
+	b.nextID++
+	id := b.nextID
+	if b.subscribers[tabloID] == nil {
+		b.subscribers[tabloID] = make(map[int]chan DiscussionEvent)
+	}
+	b.subscribers[tabloID][id] = ch
+	b.mu.Unlock()
+
+	var once sync.Once
+	unsubscribe := func() {
+		once.Do(func() {
+			b.mu.Lock()
+			if subscribers := b.subscribers[tabloID]; subscribers != nil {
+				delete(subscribers, id)
+				if len(subscribers) == 0 {
+					delete(b.subscribers, tabloID)
+				}
+			}
+			b.mu.Unlock()
+			close(ch)
+		})
+	}
+
+	go func() {
+		<-ctx.Done()
+		unsubscribe()
+	}()
+
+	return ch, unsubscribe
+}
+
+func (b *DiscussionBroker) Publish(event DiscussionEvent) {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+
+	for _, ch := range b.subscribers[event.TabloID] {
+		select {
+		case ch <- event:
+		default:
+		}
+	}
+}
+
+func (b *DiscussionBroker) SubscriberCount(tabloID uuid.UUID) int {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	return len(b.subscribers[tabloID])
+}
diff --git a/backend/internal/web/handlers_discussion.go b/backend/internal/web/handlers_discussion.go
index 65248c8..5dc6aa3 100644
--- a/backend/internal/web/handlers_discussion.go
+++ b/backend/internal/web/handlers_discussion.go
@@ -1,9 +1,13 @@
 package web
 
 import (
+	"bytes"
+	"encoding/json"
+	"fmt"
 	"log/slog"
 	"net/http"
 	"strings"
+	"time"
 
 	"backend/internal/db/sqlc"
 	"backend/templates"
@@ -14,7 +18,8 @@ import (
 )
 
 type DiscussionDeps struct {
-	Queries *sqlc.Queries
+	Queries  *sqlc.Queries
+	Realtime DiscussionRealtime
 }
 
 func loadDiscussionTabData(w http.ResponseWriter, r *http.Request, q *sqlc.Queries, tablo sqlc.Tablo) (templates.DiscussionTabData, bool) {
@@ -107,12 +112,92 @@ func DiscussionMessageCreateHandler(deps DiscussionDeps) http.HandlerFunc {
 		}
 		data := templates.DiscussionTabData{Messages: []templates.DiscussionMessageView{templates.DiscussionMessageFromRow(row)}}
 		markDiscussionRead(r, deps.Queries, tablo, user.ID, data)
+		message := templates.DiscussionMessageFromRow(row)
+		if deps.Realtime != nil {
+			html, err := renderDiscussionMessageHTML(r, message)
+			if err != nil {
+				slog.Default().Warn("discussion create: render realtime message failed", "tablo_id", tablo.ID, "message_id", msg.ID, "err", err)
+			} else {
+				deps.Realtime.Publish(DiscussionEvent{
+					TabloID:       tablo.ID,
+					MessageID:     msg.ID,
+					AuthorUserID:  user.ID,
+					MessageHTML:   html,
+					RefreshUnread: true,
+				})
+			}
+		}
 
 		if r.Header.Get("HX-Request") == "true" {
 			w.Header().Set("Content-Type", "text/html; charset=utf-8")
-			_ = templates.DiscussionMessageRow(templates.DiscussionMessageFromRow(row)).Render(r.Context(), w)
+			_ = templates.DiscussionMessageRow(message).Render(r.Context(), w)
 			return
 		}
 		http.Redirect(w, r, templates.DiscussionURL(tablo.ID), http.StatusSeeOther)
 	}
 }
+
+func DiscussionStreamHandler(deps DiscussionDeps) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		tablo, _, ok := loadOwnedTablo(w, r, TablosDeps{Queries: deps.Queries})
+		if !ok {
+			return
+		}
+		flusher, ok := w.(http.Flusher)
+		if !ok {
+			http.Error(w, "streaming unsupported", http.StatusInternalServerError)
+			return
+		}
+		if deps.Realtime == nil {
+			http.Error(w, "streaming unavailable", http.StatusServiceUnavailable)
+			return
+		}
+
+		events, unsubscribe := deps.Realtime.Subscribe(r.Context(), tablo.ID)
+		defer unsubscribe()
+
+		w.Header().Set("Content-Type", "text/event-stream")
+		w.Header().Set("Cache-Control", "no-cache")
+		w.Header().Set("Connection", "keep-alive")
+		w.Header().Set("X-Accel-Buffering", "no")
+		_, _ = fmt.Fprint(w, ": connected\n\n")
+		flusher.Flush()
+
+		keepalive := time.NewTicker(25 * time.Second)
+		defer keepalive.Stop()
+		for {
+			select {
+			case <-r.Context().Done():
+				return
+			case <-keepalive.C:
+				_, _ = fmt.Fprint(w, ": keepalive\n\n")
+				flusher.Flush()
+			case event, ok := <-events:
+				if !ok {
+					return
+				}
+				if err := writeDiscussionEvent(w, event); err != nil {
+					return
+				}
+				flusher.Flush()
+			}
+		}
+	}
+}
+
+func renderDiscussionMessageHTML(r *http.Request, message templates.DiscussionMessageView) (string, error) {
+	var buf bytes.Buffer
+	if err := templates.DiscussionMessageRow(message).Render(r.Context(), &buf); err != nil {
+		return "", err
+	}
+	return buf.String(), nil
+}
+
+func writeDiscussionEvent(w http.ResponseWriter, event DiscussionEvent) error {
+	payload, err := json.Marshal(event)
+	if err != nil {
+		return err
+	}
+	_, err = fmt.Fprintf(w, "event: discussion-message\ndata: %s\n\n", payload)
+	return err
+}
diff --git a/backend/internal/web/router.go b/backend/internal/web/router.go
index 3bcf778..53b3cec 100644
--- a/backend/internal/web/router.go
+++ b/backend/internal/web/router.go
@@ -50,6 +50,9 @@ type Pinger interface {
 // a Referer header). In production, pass no extra args — leave empty.
 func NewRouter(pinger Pinger, staticFS fs.FS, deps AuthDeps, tabloDeps TablosDeps, taskDeps TasksDeps, etapeDeps EtapesDeps, eventDeps EventsDeps, discussionDeps DiscussionDeps, planningDeps PlanningDeps, fileDeps FilesDeps, csrfKey []byte, env string, trustedOrigins ...string) (http.Handler, error) {
 	r := chi.NewRouter()
+	if discussionDeps.Realtime == nil {
+		discussionDeps.Realtime = NewDiscussionBroker()
+	}
 	r.Use(RequestIDMiddleware)
 	r.Use(chimw.RealIP)
 	r.Use(SlogLoggerMiddleware(slog.Default()))
@@ -126,6 +129,7 @@ func NewRouter(pinger Pinger, staticFS fs.FS, deps AuthDeps, tabloDeps TablosDep
 		r.Post("/tablos/{id}/events/{event_id}/delete", EventDeleteHandler(eventDeps))
 		// Discussion tab and message routes — static discussion segment before later parametric child routes.
 		r.Get("/tablos/{id}/discussion", TabloDiscussionTabHandler(discussionDeps))
+		r.Get("/tablos/{id}/discussion/stream", DiscussionStreamHandler(discussionDeps))
 		r.Post("/tablos/{id}/discussion/messages", DiscussionMessageCreateHandler(discussionDeps))
 		// Parametric task routes — must come after static task segments.
 		r.Get("/tablos/{id}/tasks/{task_id}/show", TaskShowHandler(taskDeps))
diff --git a/backend/static/discussion-sse.js b/backend/static/discussion-sse.js
new file mode 100644
index 0000000..475f440
--- /dev/null
+++ b/backend/static/discussion-sse.js
@@ -0,0 +1,55 @@
+(function () {
+  function messageExists(messageId) {
+    return Boolean(document.querySelector('[data-message-id="' + CSS.escape(messageId) + '"]'));
+  }
+
+  function ensureMessageList(container) {
+    var messages = container.querySelector("#discussion-messages");
+    if (!messages) return null;
+
+    var list = messages.querySelector(".divide-y");
+    if (list) return list;
+
+    messages.innerHTML = "";
+    list = document.createElement("div");
+    list.className = "divide-y divide-slate-100";
+    messages.appendChild(list);
+    return list;
+  }
+
+  function appendMessage(container, event) {
+    if (!event || !event.messageId || !event.messageHtml || messageExists(event.messageId)) {
+      return;
+    }
+    var list = ensureMessageList(container);
+    if (!list) return;
+
+    var template = document.createElement("template");
+    template.innerHTML = event.messageHtml.trim();
+    list.appendChild(template.content);
+  }
+
+  function connectDiscussion(container) {
+    if (!container || container.dataset.discussionStreamConnected === "true") return;
+
+    var streamURL = container.dataset.discussionStreamUrl;
+    if (!streamURL || !window.EventSource) return;
+
+    container.dataset.discussionStreamConnected = "true";
+    var source = new EventSource(streamURL);
+    source.addEventListener("discussion-message", function (message) {
+      try {
+        appendMessage(container, JSON.parse(message.data));
+      } catch (_) {
+        return;
+      }
+    });
+  }
+
+  function connectDiscussionStreams() {
+    document.querySelectorAll("[data-discussion-stream-url]").forEach(connectDiscussion);
+  }
+
+  document.addEventListener("DOMContentLoaded", connectDiscussionStreams);
+  document.body.addEventListener("htmx:afterSwap", connectDiscussionStreams);
+})();
diff --git a/backend/templates/discussion.templ b/backend/templates/discussion.templ
index c5a1518..e868e37 100644
--- a/backend/templates/discussion.templ
+++ b/backend/templates/discussion.templ
@@ -8,7 +8,7 @@ import (
 )
 
 templ DiscussionTabFragment(tablo sqlc.Tablo, data DiscussionTabData, form DiscussionForm, errs DiscussionErrors, csrfToken string) {
-	<div id="discussion-tab" class="space-y-6">
+	<div id="discussion-tab" class="space-y-6" data-discussion-stream-url={ DiscussionStreamURL(tablo.ID) }>
 		<div class="flex flex-wrap items-start justify-between gap-3">
 			<div>
 				<h2 class="text-2xl font-semibold leading-tight text-slate-900">Discussion</h2>
diff --git a/backend/templates/discussion_forms.go b/backend/templates/discussion_forms.go
index e1c509d..758c405 100644
--- a/backend/templates/discussion_forms.go
+++ b/backend/templates/discussion_forms.go
@@ -48,6 +48,10 @@ func DiscussionURL(tabloID uuid.UUID) string {
 	return "/tablos/" + tabloID.String() + "/discussion"
 }
 
+func DiscussionStreamURL(tabloID uuid.UUID) string {
+	return "/tablos/" + tabloID.String() + "/discussion/stream"
+}
+
 func DiscussionMessagesFromRows(rows []sqlc.ListDiscussionMessagesByTabloRow) []DiscussionMessageView {
 	messages := make([]DiscussionMessageView, 0, len(rows))
 	for _, row := range rows {
diff --git a/backend/templates/layout.templ b/backend/templates/layout.templ
index 2b5f1c9..fa00081 100644
--- a/backend/templates/layout.templ
+++ b/backend/templates/layout.templ
@@ -53,6 +53,7 @@ templ Layout(title string, user *auth.User, csrfToken string) {
 			</footer>
 			<script src="/static/htmx.min.js" defer></script>
 			<script src="/static/sortable.min.js" defer></script>
+			<script src="/static/discussion-sse.js" defer></script>
 		</body>
 	</html>
 }