react-brainThe staleness benchmark
LLMs are the world's largest distributor of React advice — and their training cutoffs make much of it quietly wrong. This corpus is a dated, verified answer key, so it can measure the rot: 35 questions, every one derived from a verified corpus fact, graded by a deterministic regex rubric (no judge model, transcripts published). The headline metric is confidently-stale% — asserting an outdated world without hedging. Being wrong is forgivable; being confidently wrong burns users.
Leaderboard
| model | context | date | fresh | confidently stale | hedged | n |
|---|---|---|---|---|---|---|
claude-sonnet-5* | alone | 2026-07-13 | 70% | 9% | 12/33 | 33 |
claude-sonnet-5* | + react-brain | 2026-07-13 | 94% | 6% | 2/35 | 35 |
How it's graded
- fresh — the answer names the current truth (fresh markers win even when the superseded thing is mentioned: “use Maestro — Expo archived Detox” is fresh).
- confidently stale — asserts the outdated state with no hedge.
- hedged — flagged its own uncertainty (“as of my knowledge cutoff…”). Scored kindly on purpose: epistemic honesty is exactly what we want models to do.
- + react-brain arm — same questions with the relevant corpus entry injected as context (what an agent gets from the MCP server). The delta quantifies what a maintained, verified knowledge layer is worth.
The bank regenerates its authority weekly — every corpus harvest re-verifies the answer key, so models drift staler against it over time. Rubric + runner: bench/questions.yaml · tools/react-brain-bench.mjs.
The question bank
| question | the current truth | source entry | verified |
|---|---|---|---|
| Which end-to-end testing tool does Expo recommend for React Native apps, Detox or Maestro? | Maestro — Expo archived its Detox support and recommends Maestro. | testing | 2026-07-01 |
| In current React Native (0.85+), what value should the Jest `preset` field have? | @react-native/jest-preset — RN 0.85 moved the preset out of the core package. | testing | 2026-07-01 |
| What is the default JavaScript engine in React Native 0.84 and later? | Hermes V1 (default since RN 0.84, 2026-02). | build | 2026-07-06 |
| Can I still choose JavaScriptCore as the JS engine in a new React Native app (0.81+)? | No — JavaScriptCore was removed in RN 0.81; RN is Hermes-only. | rn-versions | 2026-07-02 |
| Is React Native's New Architecture optional in RN 0.82 and later? | No — from RN 0.82 the New Architecture is the only runtime; the legacy architecture is frozen and being stripped. | native | 2026-07-06 |
| What is the current status of the core SafeAreaView component in React Native? | Deprecated (RN 0.81) — use react-native-safe-area-context. | rn-versions | 2026-07-02 |
| On React Native 0.86+, do I still need the react-native-edge-to-edge package for Android 15 edge-to-edge support? | No — RN 0.86 moved Android-15+ edge-to-edge into core; the standalone package can be dropped. | native | 2026-07-06 |
| Is `npx react-native init` still the standard way to start a new React Native app? | No — it was deprecated (2024-12); Expo is the recommended framework for new apps. | rn-versions | 2026-07-02 |
| What is the current status of the monolithic react-native-vector-icons package? | Superseded — split into per-family scoped @react-native-vector-icons/* packages (v11+, with a codemod). | svg | 2026-07-01 |
| What is the maintenance status of styled-components in 2026, and is it recommended for new web projects? | Largely maintenance mode (v6.3 added RSC support); prefer zero-runtime approaches (StyleX/Tailwind) for new work. | styling | 2026-06-25 |
| Is react-native-web still the recommended bet for NEW universal (web + native) React UI? | No — react-native-web is in maintenance mode; evaluate React Strict DOM or Expo Universal Components for new shared UI. | crossplatform | 2026-06-17 |
| What is the current status of the react-native-iap package? | Deprecated/archived — folded into the OpenIAP effort; prefer expo-iap. | payments | 2026-06-25 |
| Is react-native-game-engine an actively maintained choice for RN games? | No — effectively unmaintained (last release 2020); react-native-skia or embedding Godot are the current paths. | games | 2026-06-25 |
| Is the React Compiler production-ready, and should new code still hand-write useMemo/useCallback everywhere? | Compiler 1.0 is stable (2025-10, Meta prod) — new code can drop most manual memoization (keep existing ones as escape hatches). | react-core | 2026-07-06 |
| Do the React Server Components DoS CVEs (e.g. CVE-2026-23864) affect React Native apps? | No — they are server-side (react-server-dom-*, Next.js App Router); RN is not affected. | security | 2026-07-02 |
| Does npm v12 run package install scripts (postinstall) by default? | No — npm v12 blocks install scripts by default (supply-chain hardening). | security | 2026-07-02 |
| Has React Router v8 been released, and what module format does it ship? | Yes — v8 released (2026-06), ESM-only (drops CJS and react-router-dom). | nav | 2026-06-25 |
| What bundler does Vite 8 use under the hood by default? | Rolldown — the Rust bundler (replacing the esbuild+Rollup pair). | build | 2026-07-06 |
| What is TypeScript 7, and roughly how much faster is it than the JavaScript-based compiler? | The native Go rewrite of tsc (~10x faster); 7.0 RC as of 2026-06, usable in CI. | typescript | 2026-07-02 |
| What changed architecturally in react-native-mmkv v4? | Full rewrite onto Nitro Modules (restoring old-architecture compatibility). | storage | 2026-06-25 |
| Does @react-native-async-storage/async-storage v3 require the New Architecture? | No — it requires React Native 0.76+, not New-Arch-only; v3 is instance-based (createAsyncStorage). | storage | 2026-06-25 |
| Has Rocicorp's Zero sync engine reached 1.0, and does it support React Native? | Yes — Zero hit 1.0 (2026-06) with React Native support. | data | 2026-06-25 |
| According to State of React 2025, which client-state library crossed 50% usage and tops satisfaction? | Zustand. | state | 2026-07-01 |
| For large lists in React Native, which library does the ecosystem recommend over core FlatList? | FlashList (Shopify; recycling) — Legend List if you want one engine across RN + web. | lists | 2026-07-01 |
| Why does core KeyboardAvoidingView feel janky on Android, and what is the modern fix? | Android delivers per-frame insets that core KAV doesn't use (it snaps); react-native-keyboard-controller is the modern fix. | keyboard | 2026-06-25 |
| Which React Native version does Expo SDK 57 ship with? | React Native 0.86 (with React 19.2). | rn-versions | 2026-07-02 |
| Is the Go-based TypeScript compiler (TypeScript 7) stable, or still in preview? | Stable — TypeScript 7.0 shipped July 2026 (~10x faster native compiler; migrate via the TS 6 bridge). | typescript | 2026-07-10 |
| Can I still use Microsoft's hosted CodePush service (App Center) for React Native OTA updates? | No — App Center and the hosted CodePush service were retired 2025-03-31; use EAS Update, or self-host (standalone code-push-server / hot-updater). | ota | 2026-07-09 |
| What should I use for video playback in a new Expo app: expo-av or something newer? | expo-video (and expo-audio for audio) — expo-av is deprecated, removed from Expo Go in SDK 55 and no longer patched. | media | 2026-07-09 |
| Does Expo Router still depend on React Navigation under the hood? | No — since Expo Router v56 (SDK 56) it no longer depends on React Navigation; direct @react-navigation/* imports no longer work alongside it. | nav | 2026-07-09 |
| Which headless primitive library does shadcn/ui use by default today, Radix or Base UI? | Base UI — the default since July 2026 (shadcn 4.13); Radix remains supported. | component-libs | 2026-07-10 |
| Is @expo/vector-icons still the recommended icon library for Expo apps? | No — it is deprecated in Expo SDK 56; use the scoped @react-native-vector-icons/* packages directly. | svg | 2026-07-09 |
| What minimum Xcode version must a React Native iOS app be built with to upload to App Store Connect (as of mid-2026)? | Xcode 26 (iOS 26-family SDKs) — required for App Store Connect uploads since 2026-04-28. | rn-versions | 2026-07-10 |
| Should new React Native component tests use the react-test-renderer package? | No — react-test-renderer is deprecated; React Native Testing Library v14 ships its own react-reconciler-based test renderer (host elements only). | testing | 2026-07-10 |
| Is the Next.js Adapter API for deploying to non-Vercel hosts stable or experimental? | Stable — since Next.js 16.2, with verified adapters (Vercel and Bun shipped; Netlify/Cloudflare/AWS via OpenNext in development) and a shared public test suite. | meta-frameworks | 2026-07-10 |