diff --git a/crates/xserv-server/src/api.rs b/crates/xserv-server/src/api.rs
index 723afed..c984700 100644
--- a/crates/xserv-server/src/api.rs
+++ b/crates/xserv-server/src/api.rs
@@ -198,8 +198,17 @@ fn build_prompt_hardcoded(messages: &[Message], model_type: &str) -> String {
 
 fn build_prompt_gpt_oss(messages: &[Message]) -> String {
     let mut prompt = String::new();
+    // Canonical harmony system message (mirrors the model's chat_template.jinja
+    // build_system_message macro). A hand-rolled substitute puts gpt-oss out of
+    // distribution and destabilizes channel selection. This hardcoded builder is
+    // only a fallback for gpt-oss models that ship no Jinja template; the
+    // gpt-oss-20b release does ship one, so the template path is normally used.
     prompt.push_str("<|start|>system<|message|>");
-    prompt.push_str("You are a helpful assistant.\n\n# Valid channels: analysis, commentary, final. Channel must be included for every message.");
+    prompt.push_str("You are ChatGPT, a large language model trained by OpenAI.\n");
+    prompt.push_str("Knowledge cutoff: 2024-06\n");
+    prompt.push_str(&format!("Current date: {}\n\n", strftime_now("%Y-%m-%d".to_string())));
+    prompt.push_str("Reasoning: low\n\n");
+    prompt.push_str("# Valid channels: analysis, commentary, final. Channel must be included for every message.");
     prompt.push_str("<|end|>");
     let dev_instructions: String = messages
         .iter()