Substantial Modification (EU AI Act)
Article 3 (23) — a model update qualifies as a new act
Practitioner's note: This article is practice-oriented compliance documentation, not legal advice. We are a compliance specialist, not a law firm. For legally binding information please consult a licensed lawyer.
TL;DR
A substantial modification under Article 3 (23) of the EU AI Act is a change to an AI system after placing on the market that affects the conformity assessment or the intended purpose. Consequence: a renewed conformity assessment is required.
What is a Substantial Modification (EU AI Act)?
Examples of substantial modifications:
- Re-training a high-risk AI system with new data
- Expansion of the scope of use (e.g., from DACH to EU-wide)
- Architectural change in the AI model (added layer, algorithm change)
- Substantial improvement in accuracy beyond declared values
Not substantial: bug fixes, cosmetic UI changes, documentation updates.
Practical example
A provider of a high-risk AI recruiting tool adds a new language (FR). This is a substantial modification — a new conformity assessment is required, including a bias test on French data.
Frequently asked questions
Who decides what is 'substantial'?
The provider documents its assessment. The supervisory authority may issue a counter-assessment — the burden of proof rests with the provider.
What happens after a substantial modification?
A renewed conformity assessment, involvement of a new notified body where applicable, and an update of the technical documentation.
Downstream costs?
Conformity assessment: EUR 5,000-50,000 (in-house) or EUR 30,000-300,000 (notified body).