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title: Evolve AL Interfaces with Default Implementations in Business Central 29.0
summary: Business Central 29.0 introduces default method implementations for AL interfaces, allowing interface contracts to evolve without immediately breaking existing implementations. The feature works with RequiredPending and analyzer rules to create a staged migration path where interface authors can add new methods with fallback behavior and gradually require explicit implementations over time.
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# Evolve AL Interfaces with Default Implementations in Business Central 29.0

[Read the post](https://www.sauravdhyani.com/2026/10/evolve-al-interfaces-with-default.html) · Saurav Dhyani (Saurav Dhyani, MVP) · 2026-10-01 · 1045 words · tier community · reviewed (checked by Opus)

> Business Central 29.0 introduces default method implementations for AL interfaces, allowing interface contracts to evolve without immediately breaking existing implementations. The feature works with RequiredPending and analyzer rules to create a staged migration path where interface authors can add new methods with fallback behavior and gradually require explicit implementations over time.

## Key points

- Interfaces can now provide default method bodies, preventing immediate breaking changes when new methods are added
- RequiredPending and analyzer rules enable a staged migration where implementations gradually shift from using defaults to providing explicit implementations
- This feature reduces impact on extension ecosystems where many independent implementations depend on shared interfaces
- Default implementations should only be used when a sensible fallback behavior exists, not to avoid implementation requirements
- Interface evolution can now separate concerns between backward compatibility and controlled contract strengthening

## Quotes

- "With a default implementation, the interface method can contain a method body that provides fallback behavior." (Explains the core mechanism that enables backward compatibility when interfaces evolve)

## AL objects mentioned

As named in the post. A name that matches one object page by exact type and name links to it; the others stay as named.

- interface "INotification"

Not found in BC28-30: interface "INotification".

## Context

- Features: Default method implementations, RequiredPending attribute, Analyzer rules for interface migration, Interface contract evolution, Staged interface versioning
- Versions: Business Central 29.0, 2026 release wave 2

Source: Saurav Dhyani, community blog. Summary, key points and quotes are derived (CONTENT-NOTICE.md); read the original for the full text.