feat: stamp per-turn used model in footer stats (#6068)

Record resolved_model on assistant messages as _usedModel, expose used_model
in the usage SSE payload, and render model chips in transparent and settled
turn footers while suppressing duplicates when gateway routing already shows
used_model.

api/models.py

@@ -7989,6 +7989,7 @@ _SESSION_MESSAGE_DISPLAY_METADATA_KEYS = (
     "_turnTps",
     "_turnUsage",
     "_firstTokenMs",
+    "_usedModel",
     "_gatewayRouting",
     "_statusCard",
     "_anchor_stream_id",

api/streaming.py

@@ -9936,6 +9936,9 @@ def _run_agent_streaming(
                             _ttft_ms = meter().get_ttft_ms(stream_id)
                             if _ttft_ms is not None:
                                 _dm['_firstTokenMs'] = _ttft_ms
+                            _used_model = resolved_model or model
+                            if _used_model:
+                                _dm['_usedModel'] = _used_model
                             break
                 # Persist context window data on the session so the context-ring
                 # indicator survives a page reload (#1318). Must run BEFORE
@@ -10323,6 +10326,9 @@ def _run_agent_streaming(
             _ttft_ms = meter().get_ttft_ms(stream_id)
             if _ttft_ms is not None:
                 usage['ttft_ms'] = _ttft_ms
+            _used_model = resolved_model or model
+            if _used_model:
+                usage['used_model'] = _used_model
             # Include context window data from the agent's compressor for the UI indicator.
             # The session-level persistence happens above (before s.save()) so the values
             # survive a page reload; this block only populates the live SSE usage payload.

static/style.css

@@ -4411,6 +4411,7 @@ body.resizing .sidebar{transition:none!important;}
 .transparent-turn-footer .lf-time{color:var(--text);}
 .transparent-turn-footer .lf-sep{opacity:.4;}
 .transparent-turn-footer .lf-status{color:var(--muted);opacity:.85;}
+.transparent-turn-footer .lf-model{color:var(--muted);opacity:.85;}
 .transparent-turn-footer .lf-ttft{color:var(--accent);opacity:.9;}
 .transparent-turn-footer .lf-tokens{font-variant-numeric:tabular-nums;}
 
@@ -6110,6 +6111,7 @@ main.main > #mainPlugin{display:none;}
 .msg-usage-inline,
 .msg-duration-inline,
 .msg-gateway-inline,
+.msg-used-model-inline,
 .gateway-failover-inline,
 .msg-model-warning-inline {
   font-size: 11px;

static/ui.js

@@ -7030,6 +7030,14 @@ function _formatGatewayModelLabel(modelId,labelText,routing){
   const via=_gatewayRoutingLabel(routing);
   return via?`${base} ${via}`:base;
 }
+function _usedModelTurnChipLabel(msg){
+  if(!msg)return'';
+  const routing=msg._gatewayRouting||null;
+  if(routing&&String(routing.used_model||'').trim())return'';
+  const usedModel=String(msg._usedModel||'').trim();
+  if(!usedModel)return'';
+  return _compactComposerModelChipLabel(usedModel,getModelLabel(usedModel));
+}
 function _gatewayRoutingFailoverText(routing){
   if(!routing||!routing.has_failover)return'';
   const attempts=Array.isArray(routing.routing)?routing.routing:[];
@@ -11754,9 +11762,10 @@ function _applyTransparentRowFading(turn){
 // Mirrors the live run-status line for settled turns in transparent
 // mode. Shows duration, first-token time, token usage, and final status.
 // Only rendered for turns that have transparent event rows.
-function _transparentTurnFooterHtml(durationText, ttftText, tokensText, statusText){
+function _transparentTurnFooterHtml(durationText, modelText, ttftText, tokensText, statusText){
   const parts=[];
   if(durationText) parts.push(`<span class="lf-time">${esc(durationText)}</span>`);
+  if(modelText) parts.push(`<span class="lf-model">${esc(modelText)}</span>`);
   if(ttftText) parts.push(`<span class="lf-ttft" title="${esc(t('first_token_time')||'Time to first token')}">TTFT ${esc(ttftText)}</span>`);
   if(tokensText) parts.push(`<span class="lf-tokens">${esc(tokensText)}</span>`);
   if(statusText) parts.push(`<span class="lf-status">${esc(statusText)}</span>`);
@@ -11775,10 +11784,11 @@ function _renderTransparentTurnFooter(turn, opts){
     return;
   }
   const durationText=opts&&opts.durationText||'';
+  const modelText=opts&&opts.modelText||'';
   const ttftText=opts&&opts.ttftText||'';
   const tokensText=opts&&opts.tokensText||'';
   const statusText=opts&&opts.statusText||(t('done')||'Done');
-  const html=_transparentTurnFooterHtml(durationText, ttftText, tokensText, statusText);
+  const html=_transparentTurnFooterHtml(durationText, modelText, ttftText, tokensText, statusText);
   let footer=turn.querySelector('.transparent-turn-footer');
   if(!html){
     if(footer) footer.remove();
@@ -16595,12 +16605,13 @@ function renderMessages(options){
       // Worklog above the final answer.
       const compactWorklogForMessage=isCompactWorklogMode()&&(toolCallAssistantIdxs.has(mi)||assistantThinking.has(mi));
       const durationText=compactWorklogForMessage?'':_formatTurnDuration(msg._turnDuration);
-      if(!hasTurnUsage&&!durationText&&!gatewayText&&!failoverText&&!modelWarningText) continue;
+      const usedModelText=_usedModelTurnChipLabel(msg);
+      if(!hasTurnUsage&&!durationText&&!gatewayText&&!failoverText&&!modelWarningText&&!usedModelText) continue;
       const seg=assistantSegments.get(mi);
       const row=seg?seg.closest('.assistant-turn'):null;
       const footerRows=row?row.querySelectorAll('.msg-foot'):[];
       const targetFoot=footerRows.length?footerRows[footerRows.length-1]:null;
-      if(!targetFoot||targetFoot.querySelector('.msg-usage-inline,.msg-duration-inline,.msg-gateway-inline,.gateway-failover-inline,.msg-model-warning-inline')) continue;
+      if(!targetFoot||targetFoot.querySelector('.msg-usage-inline,.msg-duration-inline,.msg-gateway-inline,.gateway-failover-inline,.msg-model-warning-inline,.msg-used-model-inline')) continue;
       const fragments=[];
       if(modelWarningText){
         const warning=document.createElement('span');
@@ -16620,6 +16631,12 @@ function renderMessages(options){
         gateway.textContent=gatewayText;
         fragments.push(gateway);
       }
+      if(usedModelText){
+        const usedModel=document.createElement('span');
+        usedModel.className='msg-used-model-inline';
+        usedModel.textContent=usedModelText;
+        fragments.push(usedModel);
+      }
       if(durationText){
         const duration=document.createElement('span');
         duration.className='msg-duration-inline';
@@ -16676,6 +16693,7 @@ function renderMessages(options){
         // Find the corresponding message to read duration/usage.
         const seg=turn.querySelector('.assistant-segment');
         let durationText='';
+        let modelText='';
         let ttftText='';
         let tokensText='';
         if(seg){
@@ -16683,6 +16701,7 @@ function renderMessages(options){
           if(mi!=null){
             const msg=S.messages[Number(mi)]||{};
             if(msg._turnDuration!=null) durationText=_formatTurnDuration(msg._turnDuration);
+            modelText=_usedModelTurnChipLabel(msg);
             if(msg._firstTokenMs!=null) ttftText=_formatFirstToken(msg._firstTokenMs);
             if(msg._turnUsage){
               const inTok=msg._turnUsage.input_tokens||0;
@@ -16693,6 +16712,7 @@ function renderMessages(options){
         }
         _renderTransparentTurnFooter(turn,{
           durationText,
+          modelText,
           ttftText,
           tokensText,
           statusText: t('done')||'Done',

tests/test_issue6068_used_model_footer.py

@@ -0,0 +1,55 @@
+"""Regression coverage for #6068 per-turn used-model footer instrumentation."""
+
+from pathlib import Path
+
+from api.models import Session
+
+
+REPO = Path(__file__).resolve().parents[1]
+STREAMING_PY = (REPO / "api" / "streaming.py").read_text(encoding="utf-8")
+MODELS_PY = (REPO / "api" / "models.py").read_text(encoding="utf-8")
+UI_JS = (REPO / "static" / "ui.js").read_text(encoding="utf-8")
+STYLE_CSS = (REPO / "static" / "style.css").read_text(encoding="utf-8")
+
+
+def test_streaming_stamps_used_model_on_assistant_message_and_usage_payload():
+    assert "_dm['_usedModel'] = _used_model" in STREAMING_PY
+    assert "_used_model = resolved_model or model" in STREAMING_PY
+    assert "usage['used_model'] = _used_model" in STREAMING_PY
+
+
+def test_models_allowlist_round_trips_used_model_across_save_reload():
+    assert '"_usedModel"' in MODELS_PY
+    assert "_usedModel" in MODELS_PY.split("_SESSION_MESSAGE_DISPLAY_METADATA_KEYS")[1].split(")")[0]
+
+    session = Session(session_id="6068usedmodel", title="Used model")
+    session.messages = [
+        {
+            "role": "assistant",
+            "content": "done",
+            "_firstTokenMs": 250,
+            "_usedModel": "gpt-5-mini",
+        },
+    ]
+    session.save()
+
+    reloaded = Session.load("6068usedmodel")
+    assert reloaded.messages[-1]["_usedModel"] == "gpt-5-mini"
+    assert reloaded.messages[-1]["_firstTokenMs"] == 250
+
+
+def test_settled_footer_renders_used_model_chip_and_suppresses_gateway_duplicate():
+    assert "function _usedModelTurnChipLabel" in UI_JS
+    assert "msg-used-model-inline" in UI_JS
+    assert "_usedModelTurnChipLabel(msg)" in UI_JS
+    assert "routing.used_model" in UI_JS
+    assert "msg._usedModel" in UI_JS
+    assert "_compactComposerModelChipLabel(usedModel,getModelLabel(usedModel))" in UI_JS
+    assert ".msg-used-model-inline" in STYLE_CSS
+
+
+def test_transparent_turn_footer_includes_model_between_duration_and_ttft():
+    assert "function _transparentTurnFooterHtml(durationText, modelText, ttftText, tokensText, statusText)" in UI_JS
+    assert 'class="lf-model"' in UI_JS
+    assert "modelText=_usedModelTurnChipLabel(msg)" in UI_JS
+    assert ".transparent-turn-footer .lf-model" in STYLE_CSS