diff --git a/deploy/nginx/common/routes.conf b/deploy/nginx/common/routes.conf
index 30a582a1b..9ca3204ad 100644
--- a/deploy/nginx/common/routes.conf
+++ b/deploy/nginx/common/routes.conf
@@ -59,10 +59,10 @@ location ~ ^/ContentService/exporter/(diagram|document|event)/ {
     proxy_send_timeout 300s;
 }
 
-# DeltaSignal. Apache has no such route, which is why DeltaSignal cannot work on
-# beta today: the Angular side calls /api/pathways, /api/parse and /api/solve as
-# bare relative paths, routed only by proxy.conf.js — the dev server's proxy,
-# which does not exist in a built artifact.
+# DeltaSignal. The Angular side calls /api/pathways, /api/parse and /api/solve as
+# bare relative paths: proxy.conf.js routes them under the dev server, and this
+# route in a built deployment. A site profile turns the Perturb button on only
+# where one of the two exists (environments.ts, `deltaSignal`).
 location /api/ {
     include /etc/nginx/common/upstream-proxy.conf;
     proxy_pass http://deltasignal/api/;
diff --git a/projects/website-angular/src/config/environments.spec.ts b/projects/website-angular/src/config/environments.spec.ts
index cb58458c5..7003c8f5d 100644
--- a/projects/website-angular/src/config/environments.spec.ts
+++ b/projects/website-angular/src/config/environments.spec.ts
@@ -121,13 +121,13 @@ describe('site profiles', () => {
   });
 
   it('offers DeltaSignal only where a DeltaSignal backend can be reached', () => {
-    // /api is routed by proxy.conf.js, which is the dev server's proxy: it does
-    // not exist in a built artifact, and nothing in deploy.yml or the Apache
-    // config provides it. A deployment that turned this on would offer a button
-    // whose every call fails, so only `development` may have it until there is a
-    // deployed backend to point at.
+    // /api is routed by proxy.conf.js under the dev server, and by beta's nginx
+    // (deploy/nginx/common/routes.conf) to the DeltaSignal service on the same
+    // host. A deployment that turned this on without either would offer a
+    // button whose every call fails, so only those two may have it.
+    const reachable = ['development', 'beta'];
     for (const [name, profile] of Object.entries(SITE_PROFILES)) {
-      expect(profile.deltaSignal === true, `${name}.deltaSignal`).toBe(name === 'development');
+      expect(profile.deltaSignal === true, `${name}.deltaSignal`).toBe(reachable.includes(name));
     }
   });
 
diff --git a/projects/website-angular/src/config/environments.ts b/projects/website-angular/src/config/environments.ts
index f08fa2ebc..4476a00a0 100644
--- a/projects/website-angular/src/config/environments.ts
+++ b/projects/website-angular/src/config/environments.ts
@@ -182,6 +182,10 @@ export const SITE_PROFILES: Record<ProfileName, SiteProfile> = {
     searchAnswerEndpoint: '/search-answer',
     analysisSummaryEndpoint: '/analysis-summary',
     chatHandoffEndpoint: '/chat-handoff',
+    // Beta's nginx routes /api/ to the DeltaSignal service on this host
+    // (deploy/nginx/common/routes.conf), so the Perturb button's calls are
+    // answered here as they are under the dev server's proxy.
+    deltaSignal: true,
     host: 'origin',
     originFallback: 'https://beta.reactome.org',
     s3: S3,
@@ -196,10 +200,10 @@ export const SITE_PROFILES: Record<ProfileName, SiteProfile> = {
 
   development: {
     variant: 'main',
-    // The only deployment that can reach a DeltaSignal backend: proxy.conf.js
-    // routes /api to DELTASIGNAL_BACKEND, which is a dev-server proxy and does
-    // not exist in a built artifact. Turning this on elsewhere would offer a
-    // button whose every call fails, so the other profiles leave it absent.
+    // proxy.conf.js routes /api to DELTASIGNAL_BACKEND under the dev server;
+    // beta's nginx routes it the same way. Turning this on where neither
+    // proxies /api would offer a button whose every call fails, so the other
+    // profiles leave it absent.
     deltaSignal: true,
     // Same reasoning, and note the path: `/api` above already belongs to the
     // DeltaSignal backend, so the answer proxy cannot live under it.