diff --git a/src/Rest/Helpers/Channel/Channel/ThreadChannelBuilder.php b/src/Rest/Helpers/Channel/Channel/ThreadChannelBuilder.php
new file mode 100644
index 0000000..83c304e
--- /dev/null
+++ b/src/Rest/Helpers/Channel/Channel/ThreadChannelBuilder.php
@@ -0,0 +1,86 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tempcord\Discord\Rest\Helpers\Channel\Channel;
+
+use Tempcord\Discord\Rest\Helpers\Channel\Channel\Shared\SetRateLimitPerUser;
+
+/**
+ * Modifies a thread, including a post in a forum or media channel.
+ *
+ * A thread is not an ordinary channel: it has no topic, no permission
+ * overwrites and no parent to move it between, and it has archiving, locking
+ * and — in a forum — tags, which no other channel has. Passing a thread to one
+ * of the guild channel builders sends fields Discord rejects for it and offers
+ * none of the ones that actually apply.
+ *
+ * @see https://discord.com/developers/docs/resources/channel#modify-channel-json-params-thread
+ */
+class ThreadChannelBuilder extends ChannelBuilder
+{
+    use SetRateLimitPerUser;
+
+    /**
+     * The forum tags on this post, given as ids.
+     *
+     * The whole set is replaced, because that is what Discord does with the
+     * field: a tag left out of the list is a tag taken off the post. At most
+     * five, and a tag marked as moderated can only be applied by someone with
+     * Manage Threads.
+     *
+     * @param list<string> $tagIds
+     */
+    public function setAppliedTags(array $tagIds): self
+    {
+        $this->data['applied_tags'] = array_values($tagIds);
+
+        return $this;
+    }
+
+    /**
+     * @return list<string>|null
+     */
+    public function getAppliedTags(): ?array
+    {
+        return $this->data['applied_tags'] ?? null;
+    }
+
+    public function setArchived(bool $archived): self
+    {
+        $this->data['archived'] = $archived;
+
+        return $this;
+    }
+
+    /**
+     * A locked thread can still be read, but only a moderator may unarchive it.
+     */
+    public function setLocked(bool $locked): self
+    {
+        $this->data['locked'] = $locked;
+
+        return $this;
+    }
+
+    /**
+     * Whether anyone in the thread may add others to it. Private threads only.
+     */
+    public function setInvitable(bool $invitable): self
+    {
+        $this->data['invitable'] = $invitable;
+
+        return $this;
+    }
+
+    /**
+     * How long the thread sits idle before archiving itself, in minutes.
+     * Discord takes 60, 1440, 4320 or 10080.
+     */
+    public function setAutoArchiveDuration(int $minutes): self
+    {
+        $this->data['auto_archive_duration'] = $minutes;
+
+        return $this;
+    }
+}
diff --git a/tests/Rest/ChannelTest.php b/tests/Rest/ChannelTest.php
index bf512be..f0bce73 100644
--- a/tests/Rest/ChannelTest.php
+++ b/tests/Rest/ChannelTest.php
@@ -22,6 +22,7 @@
 use Tempcord\Discord\Rest\Helpers\Channel\Channel\GuildStageVoiceChannelBuilder;
 use Tempcord\Discord\Rest\Helpers\Channel\Channel\GuildTextChannelBuilder;
 use Tempcord\Discord\Rest\Helpers\Channel\Channel\GuildVoiceChannelBuilder;
+use Tempcord\Discord\Rest\Helpers\Channel\Channel\ThreadChannelBuilder;
 use Tempcord\Discord\Rest\Helpers\Channel\EditMessageBuilder;
 use Tempcord\Discord\Rest\Helpers\Channel\EditPermissionsBuilder;
 use Tempcord\Discord\Rest\Helpers\Channel\MessageBuilder;
@@ -192,6 +193,17 @@ public static function httpBindingsProvider(): array
                     'returnType' => PartsChannel::class,
                 ]
             ],
+            'Modify channel with Thread' => [
+                'method' => 'modify',
+                'args' => ['::channel id::', new ThreadChannelBuilder()],
+                'mockOptions' => [
+                    'method' => 'patch',
+                    'return' => (object) [],
+                ],
+                'validationOptions' => [
+                    'returnType' => PartsChannel::class,
+                ]
+            ],
             'Delete channel' => [
                 'method' => 'delete',
                 'args' => ['::channel id::'],
diff --git a/tests/Rest/Helpers/Channel/Channel/ThreadChannelBuilderTest.php b/tests/Rest/Helpers/Channel/Channel/ThreadChannelBuilderTest.php
new file mode 100644
index 0000000..5c545b1
--- /dev/null
+++ b/tests/Rest/Helpers/Channel/Channel/ThreadChannelBuilderTest.php
@@ -0,0 +1,81 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Tempcord\Discord\Rest\Helpers\Channel\Channel;
+
+use PHPUnit\Framework\TestCase;
+use Tempcord\Discord\Rest\Helpers\Channel\Channel\ThreadChannelBuilder;
+
+class ThreadChannelBuilderTest extends TestCase
+{
+    public function testItAppliesForumTags(): void
+    {
+        $builder = ThreadChannelBuilder::new()->setAppliedTags(['::voting::', '::urgent::']);
+
+        $this->assertSame(['applied_tags' => ['::voting::', '::urgent::']], $builder->get());
+        $this->assertSame(['::voting::', '::urgent::'], $builder->getAppliedTags());
+    }
+
+    /**
+     * Discord replaces the whole set, so the keys have to be a plain list — an
+     * array with gaps in it serialises to an object and the call is refused.
+     */
+    public function testTagsAreSentAsAList(): void
+    {
+        $tags = [3 => '::voting::', 7 => '::urgent::'];
+
+        $this->assertSame(
+            '{"applied_tags":["::voting::","::urgent::"]}',
+            json_encode(ThreadChannelBuilder::new()->setAppliedTags($tags)->get()),
+        );
+    }
+
+    public function testTakingEveryTagOffIsSaidWithAnEmptyList(): void
+    {
+        $this->assertSame(['applied_tags' => []], ThreadChannelBuilder::new()->setAppliedTags([])->get());
+    }
+
+    public function testItArchivesAndLocks(): void
+    {
+        $builder = ThreadChannelBuilder::new()->setArchived(true)->setLocked(true);
+
+        $this->assertSame(['archived' => true, 'locked' => true], $builder->get());
+    }
+
+    public function testItSetsTheIdleTimeBeforeArchiving(): void
+    {
+        $this->assertSame(
+            ['auto_archive_duration' => 1440],
+            ThreadChannelBuilder::new()->setAutoArchiveDuration(1440)->get(),
+        );
+    }
+
+    public function testItSetsWhoMayAddOthers(): void
+    {
+        $this->assertSame(['invitable' => false], ThreadChannelBuilder::new()->setInvitable(false)->get());
+    }
+
+    public function testItSetsSlowmode(): void
+    {
+        $this->assertSame(
+            ['rate_limit_per_user' => 30],
+            ThreadChannelBuilder::new()->setRateLimitPerUser(30)->get(),
+        );
+    }
+
+    public function testItRenames(): void
+    {
+        $this->assertSame(['name' => '::title::'], ThreadChannelBuilder::new()->setName('::title::')->get());
+    }
+
+    /**
+     * A thread has no channel type of its own to send, unlike every other
+     * builder here — Discord infers it from the channel being modified, and
+     * sending one is refused.
+     */
+    public function testItSendsNoChannelType(): void
+    {
+        $this->assertArrayNotHasKey('type', ThreadChannelBuilder::new()->setName('::title::')->get());
+    }
+}