Vue versions, Vapor Mode, and what changed recently

Verified 2026-08. Cross-check ../../STACK_BASELINE.md before quoting a version in an interview.

Where things stand

	Status
Vue 2	End of life since 2023-12-31. No patches, no security fixes. Migrating off it is a legitimate project to talk about.
Vue 3.5.x	Current stable (3.5.41 as of 2026-08).
Vue 3.6	Release candidate (rc.2, 2026-07-22). Vapor Mode feature-complete; reactivity rewritten on alien-signals. Not shipped stable yet — say “in RC”, not “released”.

Getting the 3.6 status right is worth doing. A candidate who says “Vue 3.6 shipped Vapor Mode” is repeating blog headlines; the accurate answer is that it is feature-complete in RC with stable expected later in 2026.

What 3.4 and 3.5 actually gave you

Recent additions that change how you write code, not just version numbers:

Version	Change	Why it matters
3.3	`defineSlots`, generic components, imported types in macros	typed component boundaries became practical
3.4	`defineModel` stable	replaces the `modelValue` prop plus `update:modelValue` emit boilerplate
3.4	faster parser, rewritten reactivity effects	fewer unnecessary re-computations
3.5	reactive props destructure	`const { x = 1 } = defineProps()` stays reactive
3.5	`useTemplateRef`, `useId`	proper template ref typing; SSR-safe ids
3.5	`onWatcherCleanup`	cleanup inside `watch` without the callback argument
3.5	lazy hydration for async components	hydrate on idle, on visible, or on interaction

If your notes still show modelValue plus emit('update:modelValue') for a two-way-bound component, they predate 3.4.

Vapor Mode

An opt-in compilation mode that compiles SFCs to imperative DOM operations with no virtual DOM. Same authoring model — templates, refs, composables — different output.

Opt-in per component, and Vapor and VDOM components interoperate in one app, so adoption is incremental rather than a rewrite.
Supports a subset of the current API. Anything depending on the VNode representation does not apply.
Smaller bundles and lower update cost, since there is no VNode allocation and no diff — reported in the range of Solid and Svelte for Vapor-only apps.
The whole runtime can be dropped from a Vapor-only build, which is where the largest bundle savings come from.

The strategic point worth making: Vue is converging with the fine-grained-reactivity camp without changing what developers write. Signals-based frameworks got there by exposing signals to the author; Vue already had refs, so only the compiler output had to change.

Alien-signals

@vue/reactivity was rewritten in 3.6 on top of alien-signals — lower overhead per dependency, better scaling in deep component trees, less memory. It is an internal change: the public ref/computed/watch API is unchanged. Mention it as evidence you follow the project, not as something that changes your code.

Migrating from Vue 2

Still a real interview topic, because plenty of production Vue 2 exists past EOL.

Vue 2	Vue 3
`Object.defineProperty` reactivity	`Proxy` — new properties and array index assignment now work, so `Vue.set` is gone
Options API only (Composition via plugin)	Composition API built in
One root node per template	fragments allowed
`filters`	removed — use computed properties or methods
`$listeners`, `.sync`	folded into `$attrs` and `v-model` arguments
`new Vue()` global config	`createApp()` — no global pollution between apps
Vuex	Pinia
`EventBus` via a Vue instance	removed; use props/emits, provide/inject, or a store

The migration build (@vue/compat) runs Vue 3 with Vue 2 behaviour and per-feature warnings, which is the incremental path. The honest framing for a large app is: upgrade the build tooling, move to the migration build, clear warnings feature by feature, then adopt Composition API where it pays — not all at once.

Interview angle

“What version of Vue would you start a project on today?” - 3.5 stable. 3.6 is in RC; you would track it and adopt Vapor Mode selectively for hot components once it ships.
“What is Vapor Mode and what does it change?” - opt-in compilation to direct DOM operations, no virtual DOM, interoperable with existing components. Bundle size and update cost drop; the authoring model does not change. It is Vue’s answer to Solid and Svelte.
“Is Vue 2 still supported?” - no, EOL since the end of 2023. Anything still on it is accruing unpatched security risk, and that is the argument you make to a product owner.
“How would you migrate a large Vue 2 app?” - migration build first, warnings cleared incrementally, then Composition API only where it earns its keep. A big-bang rewrite of a large app is how these projects die.
“What changed in 3.4/3.5 that affects how you write components?” - defineModel removed the two-way-binding boilerplate, reactive props destructure removed the props.x prefix, and useTemplateRef fixed template ref typing.