Separate iOS and Android delivery starts to get expensive long before a team decides to migrate. Features move through two implementation tracks, two review paths, two fix passes, two QA cycles, and two release schedules. On top of that, native build times in complex apps have slower feedback loops, increasing the team's time to deliver features. Which gets even more important when AI agents produce most of the app's code. The pressure builds faster when the product keeps growing while the team does not.
That delivery strain is usually what puts React Native on the table.
A migration decision changes where the risk sits during the transition. Some teams need to preserve the existing apps and move one flow at a time. Others can build a replacement on a cleaner foundation and prove parity before cutover. Some need a way to test the cleaner path without committing to it too early.
If you’re weighing those trade-offs, Migration to React Native in the AI Era helps teams pressure-test the choice before committing to a path.
Brownfield keeps the current app in production
Brownfield migration keeps the native apps as the production hosts and introduces React Native one screen or flow at a time. Users stay in the existing app while the team replaces selected product surfaces behind the same navigation, state, and release system.
This path fits products that carry high continuity risk. Session state, secure storage, push identity, subscriptions, app extensions, and platform-specific integrations often make a full replacement hard to rehearse safely. Brownfield gives teams a way to preserve that installed-app continuity while they migrate.
It also gives the organization a native fallback. A team can move gradually, test React Native in lower-risk areas first, and limit exposure while the migration workflow matures.
The cost shows up in architecture ownership. Brownfield adds a runtime boundary that somebody has to own: packaging, host integration, navigation between native and React Native, shared state, release setup, and troubleshooting. The migration takes longer when the team is maintaining the native implementation and the growing React Native surface at the same time.
Brownfield is strongest when the existing app still has to keep evolving, the native dependency surface is deep, or the business cannot absorb a risky cutover.
Greenfield gives teams a cleaner target
Greenfield migration builds a new React Native app alongside the existing product, usually on a standard foundation such as Expo. The team works toward feature parity and then ships the replacement under the existing bundle ID and package name so users receive it as an update.
This path reduces architectural drag during implementation. The target app is easier to standardize, easier to document, and easier for React Native engineers to work in. It also gives AI-assisted delivery better conditions because the patterns are more predictable and the codebase is shaped around one runtime from the start.
The risk moves to continuity and parity.
A replacement still has to preserve authentication, session continuity, deep links, secure storage, analytics, push tokens, app groups, persisted data, and every business-critical flow the existing app already handles. Mature products rarely fail because a screen cannot be rebuilt. They fail because the rebuilt app misses the accumulated behavior that users rely on. See Sonos costly migration failure as a cautionary tale.
Greenfield is strongest when continuity can be implemented and rehearsed before cutover, the native dependency surface has a credible React Native path, and the legacy app can stay under tight scope control while the new one catches up.
A checkpoint-based hybrid path gives teams room to test the cleaner option
There is also a third way to approach the decision: start greenfield, set a fixed checkpoint, and keep brownfield as a tested fallback.
It suits teams attracted to a cleaner target architecture but unwilling to treat greenfield as a leap of faith. The organization can test whether greenfield can preserve the product at a pace that justifies continuing, without funding full brownfield infrastructure before the evidence says it is necessary.
The checkpoint has to test product continuity, not only implementation speed. A few recreated screens are not enough. Teams need evidence from representative flows, including authenticated states, analytics, accessibility, performance, and at least one meaningful native boundary. The fallback also has to be real. If the team decides to move into the native hosts, packaging, navigation, state, and host integration should already be proven on a representative React Native flow.
This model works well for mature apps that want the cleaner path without treating greenfield as a leap of faith.
AI changes the tradeoff, but it does not remove the migration system
A few years ago, greenfield was often harder to justify for mature products because recovering the behavior buried in the existing codebase took too much time. Workshops and documentation rarely captured every validation rule, analytics event, fallback, and edge case. A lot of that product knowledge lived in code, release history, and lived experience.
Coding agents changed that part of the workflow.
They can inspect native implementations, trace repeated logic, and work through scoped migration tasks at a scale that was impractical before. That makes a one-to-one behavioral port more realistic than it used to be, especially when the old app stays the source of truth during the first pass. Check how Bun did it when migrating the source code from Zig to Rust.
Agents can preserve more behavior, but they do not make the migration self-governing.
A migration still needs clear mapping rules, task contracts, parity checks, device-level verification, review gates, and named human owners. The first pass should preserve behavior. The second pass should make the React Native app idiomatic. Teams that skip the second pass often end up with React Native code that still carries the structure and assumptions of the old native architecture.
AI makes greenfield more viable when the workflow is controlled. At Callstack, we combine React Native migration expertise with AI-assisted workflows that capture native behaviour, migrate scoped flows, and verify parity before scale. Without that system, a team can generate a lot of code and still learn very little about whether the migration is working.
The path decision should follow evidence, not preference
The right migration path depends on five variables:
- installed-user continuity
- native dependency surface
- legacy roadmap pressure
- verification and release exposure
- architecture ownership
Brownfield is often the safer choice when continuity is hard to reproduce outside the current hosts, native dependencies are deep, and the organization can support the extra integration layer during the transition.
Greenfield is often the better choice when the replacement can be proven before cutover, the native surface is manageable, and the team wants a simpler long-term foundation.
The checkpoint-based hybrid path fits teams that want to test greenfield under real delivery conditions while keeping a credible fallback in reserve.
What to prove before committing
A migration path deserves commitment after the team has evidence from the product itself.
That means proving the workflow on representative flows, checking whether the delivery model can preserve continuity, and showing that ownership is clear across migration artifacts, verification, release decisions, and fallback criteria.
The path decision gets sharper when teams can answer a short list of operational questions:
- Which user flows will prove whether the migration workflow works?
- Which native behaviors have to match exactly?
- Which dependencies could block a greenfield cutover?
- Which performance and continuity baselines have to hold on representative devices?
- Who owns the migration system end-to-end?
React Native migration succeeds when the delivery model is designed as carefully as the code. Brownfield, greenfield, and the hybrid checkpoint path are all valid options. The right one is the path your product can actually prove.
You can help yourself decide which path is most likely the right one for your product and organization using our dedicated migration skill:
npx skills add https://github.com/callstackincubator/agent-skills --skill assess-react-native-migrationDownload the free ebook: Migration to React Native in the AI Era
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