diff --git a/.changeset/quiet-figma-oauth-scopes.md b/.changeset/quiet-figma-oauth-scopes.md
new file mode 100644
index 000000000..71f9d6e56
--- /dev/null
+++ b/.changeset/quiet-figma-oauth-scopes.md
@@ -0,0 +1,5 @@
+---
+"@executor-js/plugin-openapi": patch
+---
+
+Do not add unadvertised OpenID Connect identity scopes to OAuth authorization requests derived from OpenAPI specifications.
diff --git a/packages/plugins/openapi/src/sdk/derive-auth.test.ts b/packages/plugins/openapi/src/sdk/derive-auth.test.ts
new file mode 100644
index 000000000..ba22b1eac
--- /dev/null
+++ b/packages/plugins/openapi/src/sdk/derive-auth.test.ts
@@ -0,0 +1,28 @@
+import { describe, expect, it } from "@effect/vitest";
+
+import { resolvedOAuthScopes } from "./derive-auth";
+
+describe("resolvedOAuthScopes", () => {
+  it("does not synthesize OIDC scopes for a plain OAuth provider", () => {
+    expect(resolvedOAuthScopes(["current_user:read", "files:read"], "auto")).toEqual([
+      "current_user:read",
+      "files:read",
+    ]);
+  });
+
+  it("preserves advertised OIDC scopes in auto mode", () => {
+    expect(resolvedOAuthScopes(["read", "openid", "profile"], "auto")).toEqual([
+      "read",
+      "openid",
+      "profile",
+    ]);
+  });
+
+  it("merges explicitly configured identity scopes", () => {
+    expect(resolvedOAuthScopes(["read", "email"], ["openid", "email"])).toEqual([
+      "read",
+      "email",
+      "openid",
+    ]);
+  });
+});
diff --git a/packages/plugins/openapi/src/sdk/derive-auth.ts b/packages/plugins/openapi/src/sdk/derive-auth.ts
index 553c8e8ca..ac7629572 100644
--- a/packages/plugins/openapi/src/sdk/derive-auth.ts
+++ b/packages/plugins/openapi/src/sdk/derive-auth.ts
@@ -41,9 +41,12 @@ const standardOidcIdentityScopes = ["openid", "email", "profile"] as const;
 
 const identityScopesForPreset = (
   identityScopes: OAuth2Preset["identityScopes"],
+  advertisedScopes: ReadonlySet<string>,
 ): readonly string[] => {
   if (identityScopes === false) return [];
-  return identityScopes === "auto" ? standardOidcIdentityScopes : identityScopes;
+  return identityScopes === "auto"
+    ? standardOidcIdentityScopes.filter((scope) => advertisedScopes.has(scope))
+    : identityScopes;
 };
 
 export const resolvedOAuthScopes = (
@@ -51,7 +54,7 @@ export const resolvedOAuthScopes = (
   identityScopes: OAuth2Preset["identityScopes"],
 ): string[] => {
   const merged = new Set(apiScopes);
-  for (const scope of identityScopesForPreset(identityScopes)) merged.add(scope);
+  for (const scope of identityScopesForPreset(identityScopes, merged)) merged.add(scope);
   return [...merged];
 };
 
@@ -141,9 +144,10 @@ const oauthTemplateFromPreset = (
 // ---------------------------------------------------------------------------
 // All spec-detected auth methods → the union of stored `Authentication`
 // templates. Header presets become apiKey templates; each oauth2 preset becomes
-// an oauth template (with its declared API scopes plus, for auth-code flows,
-// the standard identity scopes). Slugs stay deterministic per method so the
-// stored template is stable across previews of the same spec.
+// an oauth template with its declared scopes. Auto identity detection only
+// preserves standard OIDC scopes the provider advertised; it never invents
+// scopes unsupported by a plain OAuth provider. Slugs stay deterministic per
+// method so the stored template is stable across previews of the same spec.
 // ---------------------------------------------------------------------------
 
 export const detectedAuthenticationTemplates = (