diff --git a/.changeset/large-insects-own.md b/.changeset/large-insects-own.md
new file mode 100644
index 0000000000..514f393abf
--- /dev/null
+++ b/.changeset/large-insects-own.md
@@ -0,0 +1,5 @@
+---
+'@tanstack/start-server-core': patch
+---
+
+Skip a full router.update for faster createStartHandler
diff --git a/packages/start-server-core/src/createStartHandler.ts b/packages/start-server-core/src/createStartHandler.ts
index 378ed50d2d..90d4e706f9 100644
--- a/packages/start-server-core/src/createStartHandler.ts
+++ b/packages/start-server-core/src/createStartHandler.ts
@@ -584,7 +584,9 @@ export function createStartHandler<TRegister = Register>(
             getStartContext({ throwIfNotFound: false })?.requestAssets,
         })
 
-        routerInstance.update({ additionalContext: { serverContext } })
+        // `additionalContext` is request-scoped and only read from router.options
+        // during load; avoid a full router.update() and redundant location parse.
+        routerInstance.options.additionalContext = { serverContext }
         await routerInstance.load()
 
         if (routerInstance.state.redirect) {