diff --git a/libs/migrate/lib.rs b/libs/migrate/lib.rs
index 9a2e732..6edf267 100644
--- a/libs/migrate/lib.rs
+++ b/libs/migrate/lib.rs
@@ -4,6 +4,7 @@ mod m20260420_000003_add_model_id_to_room_message;
 pub mod m20260421_000001_add_agent_type_to_room_ai;
 pub mod m20260426_000001_add_thinking_content_to_room_message;
 pub mod m20260428_000001_backfill_content_tsv;
+pub mod m20260428_000002_default_use_exact_true;
 
 pub async fn execute_sql(manager: &SchemaManager<'_>, sql: &str) -> Result<(), DbErr> {
     for stmt in split_sql_statements(sql) {
@@ -93,6 +94,7 @@ impl MigratorTrait for Migrator {
             Box::new(m20260421_000001_add_agent_type_to_room_ai::Migration),
             Box::new(m20260426_000001_add_thinking_content_to_room_message::Migration),
             Box::new(m20260428_000001_backfill_content_tsv::Migration),
+            Box::new(m20260428_000002_default_use_exact_true::Migration),
             // Repo tables
             Box::new(m20250628_000028_create_repo::Migration),
             Box::new(m20250628_000029_create_repo_branch::Migration),
diff --git a/libs/migrate/m20260428_000002_default_use_exact_true.rs b/libs/migrate/m20260428_000002_default_use_exact_true.rs
new file mode 100644
index 0000000..702cc21
--- /dev/null
+++ b/libs/migrate/m20260428_000002_default_use_exact_true.rs
@@ -0,0 +1,17 @@
+use sea_orm_migration::prelude::*;
+
+#[derive(DeriveMigrationName)]
+pub struct Migration;
+
+#[async_trait::async_trait]
+impl MigrationTrait for Migration {
+    async fn up(&self, manager: &SchemaManager) -> Result<(), DbErr> {
+        let sql = include_str!("sql/m20260428_000002_default_use_exact_true.sql");
+        super::execute_sql(manager, sql).await
+    }
+
+    async fn down(&self, _manager: &SchemaManager) -> Result<(), DbErr> {
+        // No-op: data migration is non-reversible
+        Ok(())
+    }
+}
diff --git a/libs/migrate/sql/m20260428_000002_default_use_exact_true.sql b/libs/migrate/sql/m20260428_000002_default_use_exact_true.sql
new file mode 100644
index 0000000..5359dc3
--- /dev/null
+++ b/libs/migrate/sql/m20260428_000002_default_use_exact_true.sql
@@ -0,0 +1,4 @@
+-- Fix: set use_exact = true for all existing room_ai records
+-- This changes the default behavior so AI only responds when explicitly @mentioned.
+-- Previously use_exact defaulted to false, causing AI to reply to every message.
+UPDATE room_ai SET use_exact = true WHERE use_exact = false;
diff --git a/libs/room/src/ai.rs b/libs/room/src/ai.rs
index e40f2d4..2905196 100644
--- a/libs/room/src/ai.rs
+++ b/libs/room/src/ai.rs
@@ -70,7 +70,7 @@ impl RoomService {
                 active.max_tokens = Set(request.max_tokens);
             }
             if request.use_exact.is_some() {
-                active.use_exact = Set(request.use_exact.unwrap_or(false));
+                active.use_exact = Set(request.use_exact.unwrap_or(true));
             }
             if request.think.is_some() {
                 active.think = Set(request.think.unwrap_or(false));
@@ -97,7 +97,7 @@ impl RoomService {
                 system_prompt: Set(request.system_prompt),
                 temperature: Set(request.temperature),
                 max_tokens: Set(request.max_tokens),
-                use_exact: Set(request.use_exact.unwrap_or(false)),
+                use_exact: Set(request.use_exact.unwrap_or(true)),
                 think: Set(request.think.unwrap_or(false)),
                 stream: Set(request.stream.unwrap_or(false)),
                 min_score: Set(request.min_score),