diff --git a/ui/src/ui/chat-model-ref.test.ts b/ui/src/ui/chat-model-ref.test.ts
index 86b46f3fe7f..544bea8333c 100644
--- a/ui/src/ui/chat-model-ref.test.ts
+++ b/ui/src/ui/chat-model-ref.test.ts
@@ -47,4 +47,16 @@ describe("chat-model-ref helpers", () => {
     expect(resolveServerChatModelValue("gpt-5-mini", "openai")).toBe("openai/gpt-5-mini");
     expect(resolveServerChatModelValue("alias-only", null)).toBe("alias-only");
   });
+
+  it("does not double-qualify already-qualified model values", () => {
+    expect(resolveServerChatModelValue("ollama/gpt-oss:120b-cloud", "anthropic")).toBe(
+      "ollama/gpt-oss:120b-cloud",
+    );
+  });
+
+  it("preserves nested vendor/model identifiers", () => {
+    expect(
+      resolveServerChatModelValue("openrouter/anthropic/claude-sonnet-4-6", "openrouter"),
+    ).toBe("openrouter/anthropic/claude-sonnet-4-6");
+  });
 });
diff --git a/ui/src/ui/chat-model-ref.ts b/ui/src/ui/chat-model-ref.ts
index 351b8544bad..f4c4c8f4ad5 100644
--- a/ui/src/ui/chat-model-ref.ts
+++ b/ui/src/ui/chat-model-ref.ts
@@ -15,6 +15,11 @@ export function buildQualifiedChatModelValue(model: string, provider?: string |
   if (!trimmedModel) {
     return "";
   }
+  // If the model string already contains "/" it is already provider-qualified
+  // (e.g. "ollama/gpt-oss:120b-cloud"); return as-is to avoid double-qualifying.
+  if (trimmedModel.includes("/")) {
+    return trimmedModel;
+  }
   const trimmedProvider = provider?.trim();
   return trimmedProvider ? `${trimmedProvider}/${trimmedModel}` : trimmedModel;
 }
diff --git a/vitest.config.ts b/vitest.config.ts
index 568f5dd03e6..762c9ad6708 100644
--- a/vitest.config.ts
+++ b/vitest.config.ts
@@ -41,6 +41,7 @@ export default defineConfig({
       "src/**/*.test.ts",
       "extensions/**/*.test.ts",
       "test/**/*.test.ts",
+      "ui/src/ui/chat-model-ref.test.ts",
       "ui/src/ui/app-chat.test.ts",
       "ui/src/ui/views/agents-utils.test.ts",
       "ui/src/ui/views/chat.test.ts",