diff --git a/amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/chats/publicChannels/relayGroup/RelayGroupThreadsScreen.kt b/amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/chats/publicChannels/relayGroup/RelayGroupThreadsScreen.kt
index 3f4663ba3e..f49f63c876 100644
--- a/amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/chats/publicChannels/relayGroup/RelayGroupThreadsScreen.kt
+++ b/amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/chats/publicChannels/relayGroup/RelayGroupThreadsScreen.kt
@@ -70,6 +70,8 @@ import com.vitorpamplona.amethyst.ui.screen.loggedIn.chats.publicChannels.relayG
 import com.vitorpamplona.amethyst.ui.stringRes
 import com.vitorpamplona.amethyst.ui.theme.Size35dp
 import com.vitorpamplona.quartz.buzz.forum.ForumPostEvent
+import com.vitorpamplona.quartz.buzz.workspace.BUZZ_CHANNEL_TYPE_FORUM
+import com.vitorpamplona.quartz.buzz.workspace.buzzChannelType
 import com.vitorpamplona.quartz.nip01Core.core.HexKey
 import com.vitorpamplona.quartz.nip01Core.relay.normalizer.RelayUrlNormalizer
 import com.vitorpamplona.quartz.nip29RelayGroups.GroupId
@@ -99,6 +101,26 @@ fun RelayGroupThreadsScreen(
     }
 }
 
+/**
+ * Whether *starting* a thread belongs on this channel, given its Buzz `t` [channelType] (null on a
+ * relay that doesn't declare one) and whether its host speaks the Buzz dialect.
+ *
+ * On a Buzz relay the compose FAB writes a kind-45001 forum post, and Buzz only ever puts those in a
+ * `t=forum` channel — its own client mounts the forum view for `channelType === "forum"` alone, so a
+ * 45001 in a `t=stream` chat channel is a post nobody outside Amethyst can see. The relay itself
+ * accepts it (nothing there gates 45001 by channel type), which is exactly why the client has to.
+ *
+ * A Buzz channel whose kind-39000 hasn't landed yet reads as null and is treated as not-a-forum: the
+ * FAB appearing a moment later is a smaller error than publishing into the wrong channel.
+ *
+ * This gates writing only. Reading stays open on every channel — an existing thread is worth showing
+ * wherever it came from — and non-Buzz relays are untouched, where the FAB writes a NIP-7D kind-11.
+ */
+fun canStartThreadHere(
+    channelType: String?,
+    isBuzzRelay: Boolean,
+): Boolean = !isBuzzRelay || channelType == BUZZ_CHANNEL_TYPE_FORUM
+
 @Composable
 private fun RelayGroupThreads(
     channel: RelayGroupChannel,
@@ -121,7 +143,10 @@ private fun RelayGroupThreads(
 
     // Hide the compose FAB where the relay would reject the kind-11: on membership-gated groups
     // that don't list me. Open Buzz channels accept any authenticated member. See [RelayGroupChannel.canPost].
-    val canPost = channel.canPost(accountViewModel.userProfile().pubkeyHex)
+    val isBuzz = remember(channel.groupId.relayUrl) { BuzzRelayDialect.isBuzz(channel.groupId.relayUrl) }
+    val canPost =
+        channel.canPost(accountViewModel.userProfile().pubkeyHex) &&
+            canStartThreadHere(channel.event?.buzzChannelType(), isBuzz)
 
     Scaffold(
         topBar = {
@@ -153,7 +178,7 @@ private fun RelayGroupThreads(
                         // On a Buzz workspace, "new thread" is a Buzz forum post (kind 45001);
                         // vanilla NIP-29 relays use a kind-11 thread. Buzz relays reject
                         // unknown kinds, so a kind-11 thread would be refused there.
-                        if (BuzzRelayDialect.isBuzz(channel.groupId.relayUrl)) {
+                        if (isBuzz) {
                             nav.nav(Route.BuzzForumPost(channel.groupId.id, channel.groupId.relayUrl.url))
                         } else {
                             nav.nav(
@@ -178,7 +203,12 @@ private fun RelayGroupThreads(
         if (threads.isEmpty()) {
             Box(Modifier.fillMaxSize().padding(padding), contentAlignment = Alignment.Center) {
                 Text(
-                    text = stringRes(R.string.relay_group_threads_empty),
+                    text =
+                        if (canPost) {
+                            stringRes(R.string.relay_group_threads_empty)
+                        } else {
+                            stringRes(R.string.relay_group_threads_empty_read_only)
+                        },
                     style = MaterialTheme.typography.bodyMedium,
                     color = MaterialTheme.colorScheme.onSurfaceVariant,
                     modifier = Modifier.padding(32.dp),
diff --git a/amethyst/src/main/res/values/strings.xml b/amethyst/src/main/res/values/strings.xml
index eddb89c5a6..0253dfbb19 100644
--- a/amethyst/src/main/res/values/strings.xml
+++ b/amethyst/src/main/res/values/strings.xml
@@ -2636,6 +2636,8 @@
     <string name="relay_group_discovery_empty_filtered">No groups found for this filter yet.</string>
     <string name="relay_group_favorite_relay">Favorite this relay</string>
     <string name="relay_group_threads_empty">No threads yet. Start one with the + button.</string>
+    <!-- Same, where this viewer cannot start one: not a member, or a Buzz chat channel (forum posts belong to forum channels). -->
+    <string name="relay_group_threads_empty_read_only">No threads yet.</string>
     <string name="relay_group_threads_loading_older">Loading older threads…</string>
     <string name="relay_group_threads_all_caught_up">No older threads</string>
     <string name="relay_group_thread_new">New thread</string>
diff --git a/amethyst/src/test/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/chats/publicChannels/relayGroup/CanStartThreadHereTest.kt b/amethyst/src/test/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/chats/publicChannels/relayGroup/CanStartThreadHereTest.kt
new file mode 100644
index 0000000000..624d5bdf15
--- /dev/null
+++ b/amethyst/src/test/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/chats/publicChannels/relayGroup/CanStartThreadHereTest.kt
@@ -0,0 +1,68 @@
+/*
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.amethyst.ui.screen.loggedIn.chats.publicChannels.relayGroup
+
+import com.vitorpamplona.quartz.buzz.workspace.BUZZ_CHANNEL_TYPE_DM
+import com.vitorpamplona.quartz.buzz.workspace.BUZZ_CHANNEL_TYPE_FORUM
+import com.vitorpamplona.quartz.buzz.workspace.BUZZ_CHANNEL_TYPE_STREAM
+import org.junit.Assert.assertFalse
+import org.junit.Assert.assertTrue
+import org.junit.Test
+
+/**
+ * Which channels may *start* a thread. The Threads screen's compose FAB writes a Buzz kind-45001
+ * forum post on a Buzz relay and a NIP-7D kind-11 everywhere else, so the gate has to key on the
+ * channel's declared type — not just on whether the relay would accept the event, which it does.
+ *
+ * The forum case is here rather than on-device because no relay we can reach in a manual pass
+ * currently exposes a `t=forum` channel, and the allow-path is the half that must not regress: a
+ * gate that only ever denies is indistinguishable from deleting the feature.
+ */
+class CanStartThreadHereTest {
+    @Test
+    fun buzzForumChannelCanStartAThread() {
+        assertTrue(canStartThreadHere(BUZZ_CHANNEL_TYPE_FORUM, isBuzzRelay = true))
+    }
+
+    @Test
+    fun buzzChatAndDmChannelsCannot() {
+        // A 45001 here is accepted by the relay and then rendered by nobody — Buzz's own client
+        // mounts its forum view for `channelType === "forum"` alone.
+        assertFalse(canStartThreadHere(BUZZ_CHANNEL_TYPE_STREAM, isBuzzRelay = true))
+        assertFalse(canStartThreadHere(BUZZ_CHANNEL_TYPE_DM, isBuzzRelay = true))
+    }
+
+    @Test
+    fun buzzChannelWithUnknownOrUnloadedTypeCannot() {
+        // kind-39000 not in yet, or a type this version predates: fail closed rather than publish
+        // into a channel that may not be a forum.
+        assertFalse(canStartThreadHere(null, isBuzzRelay = true))
+        assertFalse(canStartThreadHere("workflow", isBuzzRelay = true))
+    }
+
+    @Test
+    fun nonBuzzRelaysAreUntouchedWhateverTheTypeSays() {
+        // Vanilla NIP-29: the FAB writes a kind-11 thread, which is valid in any group, and these
+        // relays declare no `t` at all.
+        assertTrue(canStartThreadHere(null, isBuzzRelay = false))
+        assertTrue(canStartThreadHere(BUZZ_CHANNEL_TYPE_STREAM, isBuzzRelay = false))
+    }
+}