Route-level `ssr: true` ignored when `defaultSsr: false` — staticServerFnCache not generated

[fullheart]

Which project does this relate to?

Start

Describe the bug

When defaultSsr: false is set in start.ts, route-level ssr: true is completely ignored. The staticServerFnCache is not generated during build, causing a 404 in the browser:

GET /__tsr/staticServerFnCache/...json 404 (Not Found)
Unexpected token '<', "<!DOCTYPE "... is not valid JSON

Why this matters: We want 100% client-first (defaultSsr: false) with selective SSG on specific routes — no SSR at request time. This bug makes that architecture impossible.

TanStack promise: The TanStack Start homepage states:

[...] Client-Side First [...]

This promise of "client-side first" with selective server-side capabilities (SSG) is broken when defaultSsr: false prevents route-level SSG from working.

Your Example Website or App

https://github.com/fullheart/tanstack-start-issue-selective-ssg

Two projects: ssg-working/ (defaultSsr: true) vs ssg-not-working/ (defaultSsr: false).

Steps to Reproduce the Bug or Issue

1. git clone https://github.com/fullheart/tanstack-start-issue-selective-ssg.git
2. cd ssg-not-working && npm install && npm run build
3. Check: ls .output/public/__tsr/staticServerFnCache/ → directory does not exist
4. Compare: cd ../ssg-working && npm run build && ls .output/public/__tsr/staticServerFnCache/ → file exists
5. cd ../ssg-not-working && PORT=3011 npm run start
6. Open http://localhost:3011/ssg-page in browser → you will see "Something went wrong!" and in the console:

   Failed to load resource: the server responded with a status of 404` for `__tsr/staticServerFnCache/*.json
   SyntaxError: Unexpected token '<', "<!DOCTYPE "... is not valid JSON
   

Expected behavior

• defaultSsr: false → client-first by default for all routes
• ssr: true on a route → that route should prerender and generate staticServerFnCache at build time
• The staticServerFnCache/*.json should exist for routes with ssr: true

What actually happens: defaultSsr: false prevents staticServerFnCache generation entirely. Route-level ssr: true is ignored.

Platform

• Start Version: @tanstack/react-start@1.167.42
• Router Version: @tanstack/react-router@1.168.23
• Static Server Functions: @tanstack/start-static-server-functions@1.166.33
• OS: Linux
• Bundler: Vite 8.0.9
• Nitro: 3.0.1-20260422-085752-8c3f16b2
• Node: 24.14.0

Additional context

Architecture goal: Client-first SPA (like Vite) with selective SSG for content routes. No SSR at request time.

start.ts (broken):

export const startInstance = createStart(() => ({
  defaultSsr: false
}));

ssg-page.tsx:

const fetchPost = createServerFn({ method: "GET" })
  .middleware([staticFunctionMiddleware])
  .handler(async () => {
    const res = await fetch("https://jsonplaceholder.typicode.com/posts/1");
    return await res.json();
  });

export const Route = createFileRoute("/ssg-page")({
  ssr: true,
  beforeLoad: async () => {
    const data = await fetchPost();
    return { postData: data };
  },
  component: SsgPage
});

Workaround: Set defaultSsr: true globally, but this forces SSR on all routes and defeats the purpose.

[schiller-manuel]

with defaultSsr: false you also disabled SSR on the root route, and thus all routes below it, regardless of whether ssg-page has ssr:true

see https://tanstack.com/start/latest/docs/framework/react/guide/selective-ssr#inheritance

in order to make this work, set ssr: true in the root route.

[fullheart]

@schiller-manuel Thanks, I understand — that's a design decision. I’ve opened a discussion describing what I would wish for: #7321