diff --git a/changelog.d/fixes/9435-kiro-import-overwrite.md b/changelog.d/fixes/9435-kiro-import-overwrite.md
new file mode 100644
index 0000000000..9081e7537b
--- /dev/null
+++ b/changelog.d/fixes/9435-kiro-import-overwrite.md
@@ -0,0 +1 @@
+- fix(oauth): Kiro import token endpoint no longer overwrites existing connection when using shared cached OIDC clientId (#9435)
diff --git a/src/app/api/oauth/kiro/import/route.ts b/src/app/api/oauth/kiro/import/route.ts
index 54b63d2f3e..d4b89183ab 100755
--- a/src/app/api/oauth/kiro/import/route.ts
+++ b/src/app/api/oauth/kiro/import/route.ts
@@ -217,11 +217,15 @@ export async function POST(request: Request) {
       testStatus: "active",
       isActive: true,
     };
-    const connection: any = await upsertImportedKiroConnection(targetProvider, record, {
-      profileArn: resolvedProfileArn,
-      clientId: providerSpecificData.clientId,
-      email,
-    });
+    // Only include clientId in the identity for IDC imports where it is genuinely
+    // unique per account (#2059). For Builder ID / social imports the OIDC clientId
+    // comes from a machine-wide cached OIDC registration (shared across all accounts
+    // on the same machine), so using it for identity matching would cause different
+    // accounts to overwrite each other (#9435). Without clientId, the identity
+    // matching falls through to the email field, which correctly distinguishes imports.
+    const identity: Record<string, unknown> = { profileArn: resolvedProfileArn, email };
+    if (isIdc) identity.clientId = providerSpecificData.clientId;
+    const connection: any = await upsertImportedKiroConnection(targetProvider, record, identity);
 
     // Auto sync to Cloud if enabled
     await syncToCloudIfEnabled();
diff --git a/tests/unit/kiro-import-overwrite-9435.test.ts b/tests/unit/kiro-import-overwrite-9435.test.ts
new file mode 100644
index 0000000000..d4037f7033
--- /dev/null
+++ b/tests/unit/kiro-import-overwrite-9435.test.ts
@@ -0,0 +1,87 @@
+/**
+ * TDD for #9435 — Kiro import token endpoint overwrites existing connection
+ * instead of creating new one for Builder ID / social imports.
+ *
+ * Root cause: `findKiroConnectionByIdentity` matches by cached OIDC `clientId`
+ * before `email`. When importing a second Builder ID token, the shared machine-wide
+ * cached `clientId` matches the FIRST connection instead of creating a new one.
+ *
+ * The fix: do NOT pass `clientId` in the identity object for Non-IDC (Builder ID /
+ * social) imports at the route level, so the fallback to email-based matching works.
+ */
+import test from "node:test";
+import assert from "node:assert/strict";
+
+import { findKiroConnectionByIdentity } from "../../src/lib/oauth/kiroConnectionIdentity.js";
+
+// ── Unit-level repro: the function matches by shared clientId before email ──────
+// These two connections simulate two distinct Kiro Builder ID accounts on the same
+// machine. They share a cached OIDC clientId but have different emails.
+const aliceAndBob = [
+  {
+    id: "conn-alice",
+    authType: "oauth",
+    email: "alice@example.com",
+    providerSpecificData: { clientId: "shared-cached-cid" },
+  },
+  {
+    id: "conn-bob",
+    authType: "oauth",
+    email: "bob@example.com",
+    providerSpecificData: { clientId: "shared-cached-cid" },
+  },
+];
+
+test("#9435 findKiroConnectionByIdentity with shared clientId + distinct emails: when BOTH clientId and email are passed, clientId match wins (the bug)", () => {
+  // Searching with the shared cached clientId + Bob's email.
+  // The function checks clientId FIRST so it returns conn-alice (first match by
+  // shared clientId), even though conn-bob is the correct one (email match).
+  const match = findKiroConnectionByIdentity(aliceAndBob, {
+    clientId: "shared-cached-cid",
+    email: "bob@example.com",
+  });
+  assert.equal(
+    match?.id,
+    "conn-alice",
+    `BUG: expected conn-alice (first match by shared clientId), got: ${match?.id}`
+  );
+});
+
+test("#9435 findKiroConnectionByIdentity with ONLY email (no clientId): correctly finds Bob by email", () => {
+  // When clientId is NOT in the identity (as the fix does for non-IDC imports),
+  // the function falls through to email matching and finds the right connection.
+  const match = findKiroConnectionByIdentity(aliceAndBob, {
+    email: "bob@example.com",
+  });
+  assert.equal(match?.id, "conn-bob", `expected conn-bob (email match), got: ${match?.id}`);
+});
+
+test("#9435 findKiroConnectionByIdentity with ONLY email for Alice: correctly finds Alice by email", () => {
+  const match = findKiroConnectionByIdentity(aliceAndBob, {
+    email: "alice@example.com",
+  });
+  assert.equal(match?.id, "conn-alice", `expected conn-alice (email match), got: ${match?.id}`);
+});
+
+test("#9435 findKiroConnectionByIdentity with shared clientId + new email (no match): returns null", () => {
+  // A third user with no existing connection should get null (create new connection)
+  const match = findKiroConnectionByIdentity(aliceAndBob, {
+    clientId: "shared-cached-cid",
+    email: "charlie@example.com",
+  });
+  // With clientId in the identity, it matches conn-alice (by shared clientId)
+  // instead of returning null — this IS the bug.
+  assert.equal(
+    match?.id,
+    "conn-alice",
+    `BUG: expected conn-alice (first match by shared clientId), got: ${match?.id} — charlie is new, should not match any`
+  );
+});
+
+test("#9435 findKiroConnectionByIdentity with ONLY email (no clientId) for new user: correctly returns null (create new)", () => {
+  // Without clientId, the function checks email and finds no match → null = create new
+  const match = findKiroConnectionByIdentity(aliceAndBob, {
+    email: "charlie@example.com",
+  });
+  assert.equal(match, null, `expected null for new user when no clientId, got: ${match?.id}`);
+});