ember-4-recommendations

name	ember-4-recommendations
description	Practical advice for teams settling on Ember 4.12 LTS — when to press on to 5.x, when to pause, what to invest in during the pause (Embroider, addons, TS-without-Glint). Use when triaging a 4.12 codebase, planning quarterly roadmap, or deciding the order of Embroider/TS adoption.
type	feedback

Ember 4.x — Recommendations

4.12 LTS is the last 4.x. It's a defensible resting point before the 5.x jump — much more so than 3.28 was for 3 → 4. Octane is settled; the codebase shape is the modern shape; only the build pipeline and template-authoring story (Polaris) change in 5.x.

When to pause at 4.12 vs press on

Situation	Recommendation
4.12, classic ember-cli build pipeline, no Embroider	Pause. Adopt Embroider compat first. Then 5.x.
4.12, Embroider compat, JS-typed	Press on. 5.x is straightforward from this state.
4.12, Embroider optimized	Press on. This is a textbook ready state.
4.4 / 4.8 LTS	Bump to 4.12 first.
Any 4.x with TS adopted via ember-cli-typescript	Migrate to the official TS setup before 5.x. Keeping the addon dependency complicates the bump.

Pause investments — order of operations

If you're at 4.12 and not bumping immediately, invest in this order:

1. Empty the deprecation workflow. Every silenced deprecation gets a fix or an owner.
2. Adopt Embroider compat. @embroider/core + @embroider/compat + @embroider/webpack. Settle for two weeks.
3. Audit addons for 5.x compatibility:
   • Look at each addon's repo for a 5.x compatibility statement.
   • Pin to the latest version that supports both 4.12 and 5.x.
   • Replace or fork anything stuck on 4-only.
4. Move from ember-cli-typescript (if used) to the official TS setup.
5. Type the JS layer (Registry pattern for services and models, signatures on components).
6. Move toward Embroider optimized mode — staticAddonTrees, staticHelpers, staticModifiers, staticComponents. This often surfaces dynamic-component-by-string usages that need to be made static.
7. Stop here. Bump to 5.x.

If you try to do this in a different order — e.g. adopt Glint before Embroider, or jump to 5.x with the classic build pipeline — every step gets harder.

Embroider — practical adoption

The shortest-risk path is the official three-step:

pnpm add -D @embroider/core @embroider/compat @embroider/webpack

Replace ember-cli-build.js:

'use strict';
const EmberApp = require('ember-cli/lib/broccoli/ember-app');

module.exports = function (defaults) {
  const app = new EmberApp(defaults, {
    // your existing options
  });

  const { Webpack } = require('@embroider/webpack');
  return require('@embroider/compat').compatBuild(app, Webpack, {
    // start with all flags FALSE (compat mode)
    staticAddonTrees: false,
    staticAddonTestSupportTrees: false,
    staticHelpers: false,
    staticModifiers: false,
    staticComponents: false,
    splitAtRoutes: [],
    packagerOptions: {
      webpackConfig: {}
    }
  });
};

Run the suite. Smoke-test. Once stable for a sprint, flip flags one at a time:

1. staticAddonTrees: true
2. staticAddonTestSupportTrees: true
3. staticHelpers: true
4. staticModifiers: true
5. staticComponents: true — last and hardest. Surfaces dynamic-component-by-string usages.

For each static* flag, expect to find a few dynamic-by-string usages that need to be replaced with curried component references:

{{!-- before — fails with staticComponents: true --}}
{{component this.componentName @data=foo}}

{{!-- after --}}
{{this.dynamicComponent @data=foo}}

Where this.dynamicComponent is a (component MyComponent) curried reference, not a string.

Addon hygiene at 4.12

Things to actively check:

• 5.x compatibility statement. Look in the README and package.json's peerDependencies.ember-source range.
• Glint signatures. If the addon ships them, your eventual TS adoption is much smoother.
• Embroider compatibility. Some older addons fail to compile under static modes. Check the addon's GitHub issues.
• Last release date. > 12 months stale + heavy use = fork now, don't wait.

A practical script: list addons in package.json, check each on emberobserver.com, mark each as keep / bump / replace / fork and record the decision in MIGRATION.md.

Things to keep doing

• Mirage — works the same.
• ember-test-selectors, ember-cli-page-object — keep.
• ember-power-select — keep current major.
• ember-simple-auth — keep current major (Mainmatter actively maintains).
• ember-concurrency — keep current major.
• ember-modifier — keep current major.
• ember-intl — keep current major.

Things to stop doing on 4.x

• Don't ship classic-pattern code (it doesn't compile, but addon deps sometimes sneak it in).
• Don't write (action ...) template helpers — only (fn ...) with method references.
• Don't introduce dynamic component invocation by string — Embroider optimized mode forbids it.
• Don't ignore the @embroider/macros package when an addon assumes it.

CI gates worth adding at 4.12

• tsc --noEmit (if any TS).
• template-lint --config octane (or octane:strict for stricter rules).
• eslint-plugin-ember recommended ruleset.
• Failure on new Ember.X imports.
• Bundle-size budget (Embroider tree-shakes; regressions are visible).

Backup plan before the 5.x bump

1. Tag a release/4.12 branch.
2. Tag v-pre-5-upgrade.
3. Configure CI to allow hotfixes on release/4.12.
4. Document the rollback in MIGRATION.md.

When to skip the 5.x bump and rewrite

Same heuristic as in ember-2-recommendations. If multiple are true, scope a rewrite into the latest LTS on a separate branch:

• Tests covering < 50% of user flows after the upgrade investments.
• Addon ecosystem heavily forked / bespoke.
• Build pipeline customized in ways Embroider can't absorb.
• App startup > 5s on a fast laptop, with no clear cause.
• Active product development is slowed > 30% by the upgrade burden.

The rewrite path is: build a fresh Ember 5/6 app with the ember/ plugin's conventions; route-by-route migrate the 4.x app behind a path-prefix proxy; sunset.

Verification — ready for 5.x

• On Ember 4.12.x, locked.
• ember-data 4.12.x.
• ember-cli-typescript (the addon) is removed; TS setup is official.
• All component signatures declared.
• All services and models registry-augmented.
• Embroider in at least compat mode, ideally optimized.
• All addons pinned to versions that work on both 4.12 and 5.x.
• Tests green; deprecation workflow file empty.
• CI gates against new classic patterns and bundle bloat.
• release/4.12 branch tagged.

When all green, switch to ember-4-to-5-migration.

See also

• ember-4-octane-only — what's available.
• ember-4-typescript-early — typing strategy.
• ember-4-to-5-migration — the next jump.
• The modern Ember skills (ember-octane-fundamentals, ember-polaris-migration, ember-typescript-and-glint) — the destination.