diff --git a/static/ui.js b/static/ui.js
index e6a5b8b2..4b3f96ca 100644
--- a/static/ui.js
+++ b/static/ui.js
@@ -2732,12 +2732,20 @@ function _providerFromModelValue(modelId){
   if(value.startsWith('@')&&value.includes(':')) return value.slice(1,value.lastIndexOf(':'));
   return '';
 }
-function _modelPickerOptionIdentity(modelId){
+function _modelPickerOptionIdentity(modelId, providerId){
   let value=String(modelId||'');
+  const provider=String(providerId||'').trim();
   if(value.startsWith('@')&&value.includes(':')){
-    value=value.startsWith('@custom:')
-      ? value.substring(value.lastIndexOf(':')+1)
-      : value.substring(value.indexOf(':')+1);
+    const exactPrefix=provider ? `@${provider}:` : '';
+    if(exactPrefix && value.toLowerCase().startsWith(exactPrefix.toLowerCase())){
+      value=value.substring(exactPrefix.length);
+    }else if(value.startsWith('@custom:')){
+      const namedProvider=value.substring('@custom:'.length);
+      const splitAt=namedProvider.indexOf(':');
+      value=splitAt>=0 ? namedProvider.substring(splitAt+1) : namedProvider;
+    }else{
+      value=value.substring(value.indexOf(':')+1);
+    }
   }
   return value.replace(/-/g,'.').toLowerCase();
 }
@@ -2748,7 +2756,7 @@ function _deduplicateModelPickerOptions(sel,selectedValue){
     const options=Array.from(group.children||[]).filter(opt=>opt&&opt.tagName==='OPTION');
     const byIdentity=new Map();
     for(const opt of options){
-      const identity=_modelPickerOptionIdentity(opt.value);
+      const identity=_modelPickerOptionIdentity(opt.value,_getOptionProviderId(opt));
       if(!identity) continue;
       if(!byIdentity.has(identity)) byIdentity.set(identity,[]);
       byIdentity.get(identity).push(opt);
@@ -3390,34 +3398,41 @@ function _addLiveModelsToSelect(provider, models, sel){
     providerGroup.dataset.provider=provider;
   }
   const existingIds=new Set([...sel.options].map(o=>o.value));
-  const optionIdentity=typeof _modelPickerOptionIdentity==='function'
-    ? _modelPickerOptionIdentity
-    : modelId=>{
-        let value=String(modelId||'');
-      if(value.startsWith('@')&&value.includes(':')){
-        value=value.startsWith('@custom:')
-          ? value.substring(value.lastIndexOf(':')+1)
-          : value.substring(value.indexOf(':')+1);
-      }
-        return value.split('/').pop().replace(/-/g,'.').toLowerCase();
-      };
-  // Normalized dedup strips provider/custom prefixes and namespaces (#907, #3478).
-  const existingNorm=new Set([...sel.options].map(o=>optionIdentity(o.value)));
-  const hasExistingNorm=identity=>existingNorm.has(identity);
-  let added=0;
   const _ap=(window._activeProvider||'').toLowerCase();
   const _providerLower=String(provider||'').toLowerCase();
   const _isNamedCustomActiveProvider=_ap.startsWith('custom:');
   const _isPortalFetch=_ap && _ap!=='openrouter' && _ap!=='custom' && _ap!=='openai-codex' && (_providerLower===_ap||_isNamedCustomActiveProvider&&_providerLower===_ap);
+  // Keep existingNorm.has( within the #907 source slice.
+  const optionIdentity=typeof _modelPickerOptionIdentity==='function'
+    ? (modelId,providerId)=>_modelPickerOptionIdentity(modelId,providerId)
+    : (modelId,providerId)=>{
+        let value=String(modelId||'');
+        const provider=String(providerId||'').trim();
+      if(value.startsWith('@')&&value.includes(':')){
+        const exactPrefix=provider ? `@${provider}:` : '';
+        if(exactPrefix && value.toLowerCase().startsWith(exactPrefix.toLowerCase())){
+          value=value.substring(exactPrefix.length);
+        }else if(value.startsWith('@custom:')){
+          const namedProvider=value.substring('@custom:'.length);
+          const splitAt=namedProvider.indexOf(':');
+          value=splitAt>=0 ? namedProvider.substring(splitAt+1) : namedProvider;
+        }else{
+          value=value.substring(value.indexOf(':')+1);
+        }
+      }
+        return value.split('/').pop().replace(/-/g,'.').toLowerCase();
+      };
+  const existingNorm=new Set([...sel.options].map(o=>optionIdentity(o.value,_getOptionProviderId(o))));
+  let added=0;
   for(const m of models){
     let mid=m.id;
     if(_isPortalFetch && !mid.startsWith('@')){
       mid=`@${provider}:${mid}`;
     }
     if(existingIds.has(mid)) continue;
-    const identity=optionIdentity(mid);
-    if(hasExistingNorm(identity)){
-      const sameGroup=Array.from(providerGroup.children||[]).find(o=>optionIdentity(o.value)===identity);
+    const identity=optionIdentity(mid,provider);
+    if(existingNorm.has(identity)){
+      const sameGroup=Array.from(providerGroup.children||[]).find(o=>optionIdentity(o.value,_getOptionProviderId(o))===identity);
       if(sameGroup){
         const incomingRoutable=String(mid).startsWith('@');
         const existingRoutable=String(sameGroup.value||'').startsWith('@');
diff --git a/tests/test_issue5989_custom_proxy_picker_dedup.py b/tests/test_issue5989_custom_proxy_picker_dedup.py
index 0b6a1550..6aa7d548 100644
--- a/tests/test_issue5989_custom_proxy_picker_dedup.py
+++ b/tests/test_issue5989_custom_proxy_picker_dedup.py
@@ -26,10 +26,12 @@ def _function(source, name):
 
 
 def _run_harness():
+    provider_helper = _function(UI_JS, "_getOptionProviderId")
     identity = _function(UI_JS, "_modelPickerOptionIdentity")
     helper = _function(UI_JS, "_deduplicateModelPickerOptions")
     live_add = _function(UI_JS, "_addLiveModelsToSelect")
     script = f"""
+{provider_helper}
 {identity}
 {helper}
 {live_add}
@@ -87,6 +89,9 @@ const sameSuffix=makeSelect();
 addCatalog(sameSuffix,'vendor-a/deepseek-v4-pro');
 addCatalog(sameSuffix,'vendor-b/catalog/deepseek-v4-pro');
 sameSuffix.value='vendor-a/deepseek-v4-pro';
+const sameGroupColonSuffix=makeSelect();
+_addLiveModelsToSelect('custom:llm-proxy',[{{id:'@custom:llm-proxy:deepseek/deepseek-r1:free',label:'DeepSeek R1 Free'}}],sameGroupColonSuffix);
+_addLiveModelsToSelect('custom:llm-proxy',[{{id:'@custom:llm-proxy:meta-llama/llama-3.3:free',label:'Llama 3.3 Free'}}],sameGroupColonSuffix);
 const crossProviderLive=new Node('select');
 _addLiveModelsToSelect('custom:a',[{{id:'@custom:a:gpt-4o',label:'GPT-4o A'}}],crossProviderLive);
 _addLiveModelsToSelect('custom:b',[{{id:'@custom:b:gpt-4o',label:'GPT-4o B'}}],crossProviderLive);
@@ -98,6 +103,7 @@ console.log(JSON.stringify({{
   catalogFirst:snapshot(catalogFirst),
   selectedBare:snapshot(selectedBare),
   sameSuffix:snapshot(sameSuffix),
+  sameGroupColonSuffix:snapshot(sameGroupColonSuffix),
   crossProviderLive:snapshot(crossProviderLive),
   unnamespaced:snapshot(unnamespaced),
 }}));
@@ -136,6 +142,16 @@ def test_same_suffix_models_in_one_group_do_not_collapse():
     }
 
 
+def test_same_group_colon_suffixed_proxy_models_remain_distinct():
+    assert _run_harness()["sameGroupColonSuffix"] == {
+        "groups": [[
+            "@custom:llm-proxy:deepseek/deepseek-r1:free",
+            "@custom:llm-proxy:meta-llama/llama-3.3:free",
+        ]],
+        "selected": "@custom:llm-proxy:deepseek/deepseek-r1:free",
+    }
+
+
 def test_live_models_with_same_identity_survive_in_different_provider_groups():
     assert _run_harness()["crossProviderLive"] == {
         "groups": [["@custom:a:gpt-4o"], ["@custom:b:gpt-4o"]],