diff --git a/src/main/acp/acp-dialects/omp-dialect.ts b/src/main/acp/acp-dialects/omp-dialect.ts
index 1714184b35f..0e38a7c2db5 100644
--- a/src/main/acp/acp-dialects/omp-dialect.ts
+++ b/src/main/acp/acp-dialects/omp-dialect.ts
@@ -9,6 +9,8 @@ import type { AcpDialect } from './acp-dialect'
 // background launch results do not establish a process exit.
 const textBlockSchema = z.looseObject({ type: z.literal('text'), text: z.string() })
 const promptErrorDataSchema = z.looseObject({ details: z.string() })
+// OMP's prompt check: no usable model (nothing signed in), or the selected model's provider has no key.
+const SIGNED_OUT_DETAIL_PREFIXES = ['No model selected.\n\nUse /login', 'No API key found for ']
 const toolResultSchema = z.looseObject({
   content: z.array(z.unknown()),
   details: z
@@ -95,9 +97,12 @@ function normalizeToolUpdate(update: ToolCallUpdate): ToolCallUpdate {
 export const OMP_ACP_DIALECT: AcpDialect = {
   normalizeToolUpdate,
   promptErrorDetail: (error) => promptErrorDataSchema.safeParse(error.data).data?.details,
-  authenticationRequired: (error) =>
-    error.code === -32603 &&
-    promptErrorDataSchema
-      .safeParse(error.data)
-      .data?.details.startsWith('No API key found for ') === true
+  authenticationRequired: (error) => {
+    const details = promptErrorDataSchema.safeParse(error.data).data?.details
+    return (
+      error.code === -32603 &&
+      details !== undefined &&
+      SIGNED_OUT_DETAIL_PREFIXES.some((prefix) => details.startsWith(prefix))
+    )
+  }
 }
diff --git a/src/main/acp/acp-structured-sign-in.test.ts b/src/main/acp/acp-structured-sign-in.test.ts
index 06c4b8294d1..f7349b78470 100644
--- a/src/main/acp/acp-structured-sign-in.test.ts
+++ b/src/main/acp/acp-structured-sign-in.test.ts
@@ -99,6 +99,11 @@ it.each([
     'No API key found for anthropic.\n\nUse /login, set an API key environment variable, or create /host/agent.db',
     'notSignedIn'
   ],
+  [
+    'No model selected.\n\nUse /login, set an API key environment variable, or create /host/agent.db\n\nThen use /model to select a model.',
+    'notSignedIn'
+  ],
+  ['No model selected', undefined],
   ['Rate limit exceeded', undefined],
   ['Network connection failed', undefined],
   ['No API key found elsewhere', undefined]