diff --git a/config.yaml b/config.yaml
index e735155..b400c43 100644
--- a/config.yaml
+++ b/config.yaml
@@ -179,6 +179,15 @@ model_list:
     model_info:
       mode: audio_speech
       # Tinfoil: $0 per token, $0.002 per request — see the audio section note.
+      #
+      # input_cost_per_character: 0 is load-bearing, not decoration. The TTS cost
+      # branch (cost_per_token, cost_metric == "cost_per_character") raises
+      # ValueError("cost for tts call is None") when there is no character price,
+      # and that raise aborts the whole cost calculation — so the spend write is
+      # skipped and speech bills nothing, whatever input_cost_per_request says.
+      # Declaring the zero lets the path complete; the patch then adds the
+      # per-request charge.
+      input_cost_per_character: 0
       input_cost_per_request: 0.002
 
   # --- Embedding model (Tinfoil, in-TEE) ---