diff --git a/.changeset/fix-csr-multisession-impersonation.md b/.changeset/fix-csr-multisession-impersonation.md
new file mode 100644
index 00000000000..48f4e114f79
--- /dev/null
+++ b/.changeset/fix-csr-multisession-impersonation.md
@@ -0,0 +1,6 @@
+---
+'@clerk/clerk-js': patch
+---
+
+Fix impersonation in CSR multi-session apps when admin has existing session
+
diff --git a/packages/clerk-js/src/core/clerk.ts b/packages/clerk-js/src/core/clerk.ts
index da8f4f62bb6..8a1333a7566 100644
--- a/packages/clerk-js/src/core/clerk.ts
+++ b/packages/clerk-js/src/core/clerk.ts
@@ -1456,7 +1456,14 @@ export class Clerk implements ClerkInterface {
       }
 
       if (typeof session === 'string') {
-        session = (this.client.sessions.find(x => x.id === session) as SignedInSessionResource) || null;
+        const sessionId = session;
+        session = (this.client.sessions.find(x => x.id === sessionId) as SignedInSessionResource) || null;
+        // If session not found, reload client to fetch newly created sessions (e.g., impersonation sessions)
+        // This handles the case where setActive is called immediately after creating a session via ticket
+        if (!session) {
+          await this.client.fetch();
+          session = (this.client.sessions.find(x => x.id === sessionId) as SignedInSessionResource) || null;
+        }
       }
 
       const onBeforeSetActive: SetActiveHook =