Substantial Modification (EU AI Act)
Art. 3(23) — a model update counts as a new act
TL;DR
The term legally defined in Art. 3(23) of the EU AI Act is officially 'substantial modification' (in German the official wording is 'wesentliche Veränderung', colloquially often 'wesentliche Änderung'): a change to the AI system after it has been placed on the market that was not provided for in the original conformity assessment and that affects compliance with the requirements of Chapter III, Section 2, or results in a change to the intended purpose. Consequence: a further conformity assessment is required.
What is a substantial modification (EU AI Act)?
The EU AI Act defines this term officially in Art. 3(23) as a 'substantial modification': a change to an AI system after its placing on the market or putting into service which is not foreseen or planned in the initial conformity assessment carried out by the provider and as a result of which compliance with the requirements of Chapter III, Section 2 is affected, or which results in a modification to the intended purpose. The colloquial German label 'wesentliche Änderung' refers to the same legal consequence; the legal term in the text of the Regulation (Art. 3(23)) is, however, 'wesentliche Veränderung'.
Germany and Austria: The term comes from the AI Act (Regulation (EU) 2024/1689) and applies equally in Germany and Austria; as a directly applicable EU regulation, the definition is applied with identical wording in both jurisdictions (no national transposition margin).
Examples of substantial modifications:
- Re-training a high-risk AI system with new data
- Extending the area of use (for example from DACH to EU-wide)
- Architectural change in the AI model (adding a layer, changing the algorithm)
- Substantial improvement in accuracy beyond the declared values
Not substantial: bug fixes, cosmetic UI changes, documentation updates.
Example from practice
The provider of a high-risk AI recruiting tool adds a new language (FR). That is a substantial modification within the meaning of Art. 3(23) — a new conformity assessment with a bias test on French data is required.