Forward Compatibility in eCTD v4 – How to Carry Your Current eCTD v3 Application History Into the Future

Forward compatibility in eCTD v4 allows organizations baseline lifecycle continuity between current eCTD v3 applications and the new v4 format. By linking content and structure without the need for a baseline submission to the regulator, regulatory teams can ensure lifecycle integrity, reduce duplication, and avoid errors. This post explains what forward compatibility is, why it matters for the global adoption of eCTD v4 submissions, and why now is the time to prepare.

The Change Is Coming

If your regulatory submissions were a road network, eCTD v3 is the road you’ve been traveling for years – familiar lanes, well-known signs, predictable stops. Now, authorities are introducing eCTD v4, which is a faster, more modern system. This sounds great, but there is a challenge: how do you preserve the work you’ve already submitted in v3?

Forward compatibility is the solution. It connects your existing infrastructure and submission content to the new v4 format, so your regulatory history remains intact and readable as a single continuous application.

What Is Forward Compatibility?

Forward compatibility allows an eCTD v4 submission to reference documents originally submitted in eCTD v3 without needing to re-upload them. For scientific assessors and reviewers, this means they can view one cohesive application rather than separate v3 and v4 histories.

Technically, this is achieved by:

• Referencing the original v3 leaf IDs correctly.
• Using the appropriate OID namespace for v3.
• Matching the context of use and keywords exactly to the eCTD v3.

These elements retain the lifecycle chain, preventing breaks or errors.

Why This Matters Now

Regulatory authorities are moving forward with eCTD v4 at different speeds and with different approaches to forward compatibility:

• EMA: Are the first global regulator to pilot Forward Compatibility for Centralised Procedures. Phased rollout is in progress; mandatory for initial centrally authorized products from 2026, with forward compatibility supported in the upcoming pilot.
• US FDA: Accepting eCTD v4 applications since September 2024, with forward compatibility enabling v3 content to link automatically. Please note that their dedicated forward compatibility pilot is planned for 2026.
• PMDA (Japan): eCTD v4 is accepted, but there is currently no forward compatibility mechanism. Current v3 content applications must be managed in parallel manually.

For companies managing large portfolios, this distinction is crucial. Forward compatibility allows US FDA and EMA submissions to maintain application continuity automatically. Without it, as with PMDA, every update could require resubmitting already approved content — much like having to reprint an entire book just to add a new chapter. For organizations with hundreds of v3 sequences, forward compatibility avoids additional workload to maintain multiple standards, all while ensuring that regulatory submissions remain a single, continuous story.

The Benefits of Forward Compatibility

Implementing forward compatibility in eCTD v4 delivers tangible benefits across regulatory operations:

• Continuity: The application maintains a single, coherent lifecycle and structure across v3 and v4 sequences, allowing reviewers to trace document history without interruption.
• Efficiency: By reusing previously submitted content, regulatory teams avoid redundant re-publication of baseline submissions, minimize manual reconciliation of sequences, and reduce the workload associated with managing medicine portfolio updates.
• Lower Risk: Forward compatibility prevents broken lifecycle chains and improves the quality of submissions by reducing the likelihood of validation errors.
• Improved Reviewer and Team Experience: Regulators assess applications with full historical lifecycle, improving assessment quality and speed. Internal teams benefit from smoother publishing workflows, automated validations, and simplified document management across multiple silos.

Forward compatibility is more than a technical feature; it is a strategic capability that preserves regulatory integrity and ensures robust portfolio governance.

By establishing a forward-compatible framework, organizations strengthen their submission strategy, maintain compliance across authorities, and create a foundation for scalable regulatory operations.

Your next stop towards Forward Compatibility – Part II:

In Part II of this series, we will go under the hood: how forward compatibility works technically and what common pitfalls to avoid when bridging your eCTD v3 and eCTD v4 submissions:  Forward Compatibility in eCTD v4 – The Bridge to eCTD v4 | EXTEDO