From 57e69e9dec3a5dcb62e84afe24e3b10c6633e1a7 Mon Sep 17 00:00:00 2001
From: ladybluenotes <hello@sarahgerrard.me>
Date: Thu, 10 Sep 2026 19:18:47 -0700
Subject: [PATCH 1/2] perf(history): avoid generating unused location keys

---
 .changeset/lazy-locations-listen.md      |  5 +++++
 packages/history/src/index.ts            |  8 +++++---
 packages/history/tests/parseHref.test.ts | 24 ++++++++++++++++++++++++
 3 files changed, 34 insertions(+), 3 deletions(-)
 create mode 100644 .changeset/lazy-locations-listen.md

diff --git a/.changeset/lazy-locations-listen.md b/.changeset/lazy-locations-listen.md
new file mode 100644
index 0000000000..d048bbebe4
--- /dev/null
+++ b/.changeset/lazy-locations-listen.md
@@ -0,0 +1,5 @@
+---
+'@tanstack/history': patch
+---
+
+Avoid generating unused history keys for locations with existing state.
diff --git a/packages/history/src/index.ts b/packages/history/src/index.ts
index b8fd3f016c..29ee775191 100644
--- a/packages/history/src/index.ts
+++ b/packages/history/src/index.ts
@@ -749,8 +749,10 @@ export function parseHref(
   const sanitizedHref = normalizeHref(href)
   const hashIndex = sanitizedHref.indexOf('#')
   const searchIndex = sanitizedHref.indexOf('?')
-
-  const addedKey = createRandomKey()
+  if (!state) {
+    const key = createRandomKey()
+    state = { [stateIndexKey]: 0, key, __TSR_key: key }
+  }
 
   return {
     href: sanitizedHref,
@@ -772,7 +774,7 @@ export function parseHref(
             hashIndex === -1 ? undefined : hashIndex,
           )
         : '',
-    state: state || { [stateIndexKey]: 0, key: addedKey, __TSR_key: addedKey },
+    state,
   }
 }
 
diff --git a/packages/history/tests/parseHref.test.ts b/packages/history/tests/parseHref.test.ts
index e1a95fafa4..10df49d330 100644
--- a/packages/history/tests/parseHref.test.ts
+++ b/packages/history/tests/parseHref.test.ts
@@ -21,6 +21,30 @@ describe('parseHref', () => {
     expect(parsed.hash).toEqual('#qux')
   })
 
+  test.each([
+    { __TSR_index: 2 },
+    { __TSR_index: 2, key: 'legacy-key', __TSR_key: 'current-key' },
+  ])('preserves supplied state %j', (state) => {
+    Object.freeze(state)
+    expect(parseHref('/foo', state).state).toBe(state)
+  })
+
+  test('creates independent initial states with matching history keys', () => {
+    const first = parseHref('/foo', undefined)
+    const second = parseHref('/bar', undefined)
+
+    for (const location of [first, second]) {
+      expect(location.state).toEqual({
+        __TSR_index: 0,
+        key: expect.any(String),
+        __TSR_key: location.state.key,
+      })
+    }
+
+    first.state.__TSR_index = 1
+    expect(second.state.__TSR_index).toBe(0)
+  })
+
   describe('open redirect prevention', () => {
     test('strips CR characters to prevent open redirect', () => {
       // If \r (CR) is in the href, it should be stripped

From a2f58a3d9ac5b058a4381f817b5e64238565aa59 Mon Sep 17 00:00:00 2001
From: Sarah Gerrard <gerrardsarah@gmail.com>
Date: Sat, 12 Sep 2026 13:15:57 -0700
Subject: [PATCH 2/2] refactor(history): drop redundant empty-state fallback in
 assignKeyAndIndex

Spreading undefined is a no-op, so the guard was dead weight.
---
 packages/history/src/index.ts | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/packages/history/src/index.ts b/packages/history/src/index.ts
index 29ee775191..1c9bd5ed18 100644
--- a/packages/history/src/index.ts
+++ b/packages/history/src/index.ts
@@ -281,9 +281,6 @@ export function createHistory(opts: {
 }
 
 function assignKeyAndIndex(index: number, state: HistoryState | undefined) {
-  if (!state) {
-    state = {}
-  }
   const key = createRandomKey()
   return {
     ...state,