diff --git a/experiments/field_trials.py b/experiments/field_trials.py
index 6fd3d04..5949cdc 100755
--- a/experiments/field_trials.py
+++ b/experiments/field_trials.py
@@ -155,6 +155,9 @@
     FieldTrial('WebRTC-Video-H26xPacketBuffer',
                41480904,
                date(2024, 6, 1)),
+    FieldTrial('WebRTC-Video-Vp9FlexibleMode',
+               329396373,
+               date(2025, 6, 26)),
     # keep-sorted end
 ])  # yapf: disable
 
diff --git a/media/engine/webrtc_video_engine.cc b/media/engine/webrtc_video_engine.cc
index 70176e8..33ad546 100644
--- a/media/engine/webrtc_video_engine.cc
+++ b/media/engine/webrtc_video_engine.cc
@@ -978,10 +978,8 @@
           {{"off", webrtc::InterLayerPredMode::kOff},
            {"on", webrtc::InterLayerPredMode::kOn},
            {"onkeypic", webrtc::InterLayerPredMode::kOnKeyPic}});
-      webrtc::FieldTrialFlag force_flexible_mode("FlexibleMode");
       webrtc::ParseFieldTrial(
-          {&interlayer_pred_experiment_enabled, &inter_layer_pred_mode,
-           &force_flexible_mode},
+          {&interlayer_pred_experiment_enabled, &inter_layer_pred_mode},
           call_->trials().Lookup("WebRTC-Vp9InterLayerPred"));
       if (interlayer_pred_experiment_enabled) {
         vp9_settings.interLayerPred = inter_layer_pred_mode;
@@ -989,7 +987,10 @@
         // Limit inter-layer prediction to key pictures by default.
         vp9_settings.interLayerPred = webrtc::InterLayerPredMode::kOnKeyPic;
       }
-      vp9_settings.flexibleMode = force_flexible_mode.Get();
+
+      // TODO(webrtc:329396373): Remove after flexible mode is fully deployed.
+      vp9_settings.flexibleMode =
+          IsDisabled(call_->trials(), "WebRTC-Video-Vp9FlexibleMode");
     } else {
       // Multiple spatial layers vp9 screenshare needs flexible mode.
       vp9_settings.flexibleMode = vp9_settings.numberOfSpatialLayers > 1;
@@ -1503,9 +1504,9 @@
   RTC_DCHECK(ssrc != 0);
   send_streams_[ssrc] = stream;
 
-    if (ssrc_list_changed_callback_) {
-      ssrc_list_changed_callback_(send_ssrcs_);
-    }
+  if (ssrc_list_changed_callback_) {
+    ssrc_list_changed_callback_(send_ssrcs_);
+  }
 
   if (sending_) {
     stream->SetSend(true);
@@ -3146,22 +3147,22 @@
     // BWE has already been notified of this received packet.
     return false;
   }
-    // Ignore unknown ssrcs if we recently created an unsignalled receive
-    // stream since this shouldn't happen frequently. Getting into a state
-    // of creating decoders on every packet eats up processing time (e.g.
-    // https://crbug.com/1069603) and this cooldown prevents that.
-    if (last_unsignalled_ssrc_creation_time_ms_.has_value()) {
-      int64_t now_ms = rtc::TimeMillis();
-      if (now_ms - last_unsignalled_ssrc_creation_time_ms_.value() <
-          kUnsignaledSsrcCooldownMs) {
-        // We've already created an unsignalled ssrc stream within the last
-        // 0.5 s, ignore with a warning.
-        RTC_LOG(LS_WARNING)
-            << "Another unsignalled ssrc packet arrived shortly after the "
-            << "creation of an unsignalled ssrc stream. Dropping packet.";
-        return false;
-      }
+  // Ignore unknown ssrcs if we recently created an unsignalled receive
+  // stream since this shouldn't happen frequently. Getting into a state
+  // of creating decoders on every packet eats up processing time (e.g.
+  // https://crbug.com/1069603) and this cooldown prevents that.
+  if (last_unsignalled_ssrc_creation_time_ms_.has_value()) {
+    int64_t now_ms = rtc::TimeMillis();
+    if (now_ms - last_unsignalled_ssrc_creation_time_ms_.value() <
+        kUnsignaledSsrcCooldownMs) {
+      // We've already created an unsignalled ssrc stream within the last
+      // 0.5 s, ignore with a warning.
+      RTC_LOG(LS_WARNING)
+          << "Another unsignalled ssrc packet arrived shortly after the "
+          << "creation of an unsignalled ssrc stream. Dropping packet.";
+      return false;
     }
+  }
 
   // RTX SSRC not yet known.
   ReCreateDefaultReceiveStream(packet.Ssrc(), absl::nullopt);