Competition Law and Behavioural Interoperability Obligations

1. Introduction

Behavioural interoperability obligations are competition-law obligations requiring a dominant undertaking, platform, infrastructure operator, or other market-power holder to modify its conduct so that competing products, services, applications, systems, or networks can interact effectively with its ecosystem.

The central competition concern is that a firm may possess control over an essential interface, operating system, technical protocol, API, data environment, network, or platform and use that control to disadvantage competitors. Interoperability obligations seek to prevent the dominant firm from converting control over one layer of the market into durable power over adjacent markets.

Traditional competition law generally intervenes after anti-competitive conduct has been established. Behavioural interoperability regulation can be more proactive: it may require the undertaking to provide access, disclose technical information, maintain compatibility, avoid discriminatory access conditions, or permit rival services to use functionality available to the undertaking's own services.

The European Union's Digital Markets Act illustrates this shift particularly clearly. Article 6(7) requires designated gatekeepers operating relevant operating systems to provide third parties with effective interoperability with hardware and software features available to the gatekeeper's own services.

2. Meaning of Interoperability

Interoperability means the ability of independent systems, products, applications or services to communicate, interact and function together.

It may involve:

1. Technical interoperability – APIs, protocols, interfaces and communication standards.
2. Data interoperability – ability to access, transfer or use data in compatible formats.
3. Functional interoperability – a rival service can use functionality controlled by the dominant platform.
4. Network interoperability – users of competing networks can communicate with each other.
5. Operating-system interoperability – third-party applications can access OS capabilities.
6. Messaging interoperability – users of different messaging services can communicate.
7. Device interoperability – third-party hardware can interact with a dominant operating system.
8. Platform interoperability – competing services can operate alongside a dominant platform without artificial technical restrictions.

Thus, interoperability is not simply a technical engineering issue. In concentrated markets, it can become a competition-law remedy and regulatory obligation.

3. Why Behavioural Interoperability Matters in Competition Law

Interoperability becomes a competition issue particularly where a firm controls a bottleneck.

A simplified structure is:

Dominant platform → essential interface → complementary services → consumers

If the platform gives its own service full access but prevents rivals from obtaining comparable access, several competitive problems may arise.

A. Foreclosure

The dominant undertaking can prevent rivals from effectively competing.

B. Ecosystem lock-in

Consumers may remain within an ecosystem because competing services cannot reproduce the same functionality.

C. Network effects

A large installed user base can reinforce the incumbent's position.

D. Switching costs

Users may face technical or functional costs when moving to a competing service.

E. Self-preferencing

The platform may give its own downstream service superior technical access.

F. Innovation foreclosure

Innovative competitors may be unable to develop products because critical platform functionality is unavailable to them.

G. Raising rivals' costs

Even where access technically exists, excessive fees, delays, inferior technical specifications or discriminatory conditions can make effective competition impossible.

4. Behavioural Interoperability vs Structural Remedies

Competition law traditionally has two broad approaches.

Structural remedy

The undertaking's structure is changed—for example, divestiture or separation of businesses.

Behavioural remedy

The undertaking remains intact but is required to change its conduct.

Interoperability obligations are generally behavioural remedies.

For example, a dominant operating-system provider may be required to:

• disclose APIs;
• provide technical documentation;
• permit access to interfaces;
• provide equivalent functionality to rivals;
• avoid discriminatory access;
• maintain compatibility;
• provide access on reasonable terms;
• respond within defined time periods;
• preserve interoperability following software updates.

The United States Microsoft litigation provides a particularly clear historical example of such obligations. The final judgment required disclosure of APIs, communications interfaces and technical information necessary for third-party products to interoperate with Windows.

5. Legal Foundations

A. Abuse of Dominance

Under traditional competition law, interoperability obligations can arise through abuse-of-dominance principles.

In the EU, Article 102 TFEU can address conduct such as:

• refusal to supply;
• discriminatory access;
• tying;
• technical restrictions;
• exclusionary conduct;
• leveraging dominance into neighbouring markets.

The difficulty is that a refusal to deal is not automatically unlawful.

This is why the jurisprudence concerning essential facilities and refusal to supply is important.

B. Essential-Facilities Principles

Where a dominant undertaking controls infrastructure or an input that competitors cannot realistically reproduce, competition law may, in exceptional circumstances, require access.

However, courts have traditionally been cautious because an unrestricted interoperability obligation can weaken:

• property rights;
• incentives to invest;
• incentives to innovate;
• product development incentives.

Consequently, courts have developed relatively demanding tests for compulsory access.

C. Digital Markets Regulation

The EU Digital Markets Act moves beyond the traditional exceptional-refusal-to-deal model.

Article 6(7) DMA requires designated gatekeepers to provide effective interoperability with relevant hardware and software features controlled by their operating systems. The Commission describes the purpose as ensuring that third parties can compete on equal terms with the gatekeeper's own services.

The Commission has also developed specification proceedings, where it can specify how interoperability must actually be implemented.

In July 2026, the Commission adopted binding measures concerning Google's Android interoperability for competing AI services.

6. Core Behavioural Interoperability Obligations

6.1 Non-Discriminatory Access

A dominant undertaking should not provide its own downstream service with superior access while providing competitors with inferior functionality.

The relevant comparison is often:

Dominant firm's service access ≠ Rival's restricted access

If the difference cannot be objectively justified, discrimination may create exclusionary effects.

6.2 Equal-Effectiveness Principle

Formal access is insufficient if the rival cannot actually use the interface effectively.

For example:

API technically available + severe latency + incomplete functionality = potentially ineffective interoperability.

Therefore, modern interoperability regulation increasingly focuses on effective, rather than merely nominal, access.

The DMA expressly uses the concept of effective interoperability.

6.3 Timely Access

Delay can itself become an exclusionary strategy.

A platform might provide technical information only after its own competing product has entered the market.

Therefore, an interoperability obligation may require:

• prompt responses;
• technical documentation;
• advance notice of changes;
• timely API disclosure;
• reasonable implementation periods.

6.4 Technical Documentation

Competitors may need:

• APIs;
• protocols;
• data formats;
• authentication procedures;
• communication specifications;
• software development documentation.

The historical Microsoft proceedings demonstrate the importance of such information in allowing competing software to interact with Windows.

6.5 Non-Discrimination

Access should not be conditioned on discriminatory commercial arrangements.

Possible discriminatory practices include:

• higher prices for rivals;
• inferior technical specifications;
• delayed access;
• selective API availability;
• restrictive licensing;
• discriminatory authentication;
• preferential treatment for the platform's own applications.

6.6 Functional Parity

A particularly important concept in digital markets is functional parity.

Suppose a platform gives its own AI assistant the ability to:

• invoke system functions;
• read relevant contextual information;
• interact with applications;
• execute tasks;
• access device functionality,

while rival AI systems cannot.

A competition regulator may examine whether denying those capabilities makes effective competition impossible.

The Commission's 2026 Android proceedings specifically addressed interoperability for competing AI services, including access to Android capabilities used by Google's own AI services.

7. Six Important Case Laws

Case 1: Microsoft Corp. v Commission, Case T-201/04

Court: Court of First Instance / General Court of the EU
Year: 2007

Facts

Microsoft possessed a dominant position in client PC operating systems. The European Commission found that Microsoft had refused to provide competitors with interoperability information necessary for competing work-group server products.

Legal issue

Whether Microsoft's refusal to supply interoperability information constituted an abuse of dominant position.

Decision

The Court substantially upheld the Commission's findings concerning Microsoft's refusal to supply interoperability information and the resulting exclusionary effects.

Importance

This is one of the most important interoperability cases in competition law.

It demonstrates that interoperability information can itself constitute a strategically important competitive input.

Principle

A dominant undertaking controlling a technologically important interface may, in exceptional circumstances, be required to provide information necessary for effective competition.

Case 2: United States v Microsoft Corp.

Court: U.S. District Court / U.S. Court of Appeals
Period: 1998–2001 and subsequent remedies

Facts

Microsoft was found to have unlawfully maintained its monopoly in PC operating systems through exclusionary practices affecting competing middleware.

The proceedings ultimately produced extensive behavioural obligations.

Interoperability remedy

The final judgment required Microsoft to disclose APIs, communications interfaces and technical information necessary for third-party interoperability with Windows.

The U.S. Department of Justice subsequently noted that certain interoperability provisions had been extended during enforcement of the judgment.

Importance

The case illustrates how antitrust remedies can move beyond merely prohibiting conduct and impose continuing technical obligations.

Principle

Competition remedies can require a dominant technology platform to provide sufficient technical transparency to permit rival products to interoperate.

Case 3: Oscar Bronner GmbH v Mediaprint, Case C-7/97

Court: Court of Justice of the European Union
Year: 1998

Facts

Bronner, a newspaper publisher, sought access to Mediaprint's newspaper home-delivery system.

Issue

Whether refusal to provide access to the delivery system constituted an abuse of dominance.

Decision

The Court applied a strict test for compulsory access. Among the important considerations was whether the infrastructure was indispensable and whether duplication was economically or technically feasible.

Importance

Bronner establishes an important limitation on interoperability/access obligations.

Competition law should not automatically require every dominant undertaking to share its infrastructure.

Principle

An access obligation normally requires exceptional circumstances, particularly where the requested facility is indispensable and cannot realistically be duplicated.

Case 4: IMS Health GmbH & Co. OHG v NDC Health, Case C-418/01

Court: Court of Justice of the European Union
Year: 2004

Facts

IMS Health controlled a copyright-protected system used for pharmaceutical sales data.

A competitor sought access to the relevant structure in order to compete.

Issue

Whether refusal to license intellectual-property rights could constitute abuse of dominance.

Decision

The Court reaffirmed the exceptional nature of compulsory licensing but identified circumstances in which refusal to license intellectual property could constitute an abuse. The case is part of the jurisprudence governing access to indispensable inputs and interoperability-related interfaces.

Importance

IMS Health demonstrates the tension between:

• intellectual-property protection; and
• competition through access.

Principle

Interoperability obligations must carefully balance the preservation of innovation incentives against the need to prevent exclusionary control over indispensable inputs.

Case 5: Slovak Telekom v Commission, Case C-165/19 P

Court: Court of Justice of the European Union
Year: 2021

Facts

Slovak Telekom, the incumbent telecommunications operator, was subject to regulatory obligations concerning access to its local loop.

The Commission examined conditions imposed on alternative operators seeking access.

Issue

Whether conditions attached to access could constitute abusive conduct under Article 102 TFEU.

Decision

The Court addressed the interaction between regulatory access obligations and Article 102 TFEU, including issues surrounding access, margin squeeze and the indispensability requirement.

Importance

This case is particularly important for regulated interoperability.

It demonstrates that an undertaking cannot necessarily avoid competition-law scrutiny merely because access is also governed by sectoral regulation.

Principle

Competition law and sector-specific interoperability/access regulation can operate together.

Case 6: Google Android, T-604/18 and C-738/22 P

Court: General Court and Court of Justice of the European Union
General Court: 2022
Court of Justice: 2026

Facts

The Google Android proceedings concerned Google's conduct involving Android, Google Search, Google Play and contractual restrictions imposed on device manufacturers and operators.

The General Court largely upheld the Commission's findings concerning Google's restrictions, including anti-fragmentation obligations and conduct affecting alternative Android operating systems.

The Court of Justice delivered its appeal judgment on 2 July 2026.

Importance for interoperability

The case illustrates how control over an operating-system ecosystem can affect the ability of alternative services and operating-system variants to develop.

It is especially relevant to:

• platform ecosystems;
• Android forks;
• technical compatibility;
• contractual restrictions;
• network effects;
• leveraging dominance across connected markets.

Principle

Competition analysis in digital ecosystems may examine not merely a single product but the interaction between operating systems, app stores, search services, applications and contractual restrictions.

8. The Emerging DMA Approach

The Digital Markets Act represents a significant development because interoperability is increasingly treated as a direct regulatory obligation, rather than relying entirely on an Article 102-style refusal-to-deal case.

Under Article 6(7), designated gatekeepers must provide third parties with effective interoperability with hardware and software features available to the gatekeeper's own services.

This has important consequences.

Traditional model

Dominance → abusive refusal → investigation → infringement decision → remedy

Behavioural interoperability model

Gatekeeper designation → statutory interoperability duty → technical request → compliance/specification → monitoring/enforcement

This can reduce the evidentiary burden associated with proving a traditional refusal-to-deal abuse.

9. Behavioural Interoperability and AI

AI platforms make interoperability particularly important.

Consider a dominant mobile operating system with an integrated AI assistant.

The platform's own AI service may receive privileged access to:

• device context;
• application functions;
• notifications;
• system controls;
• search data;
• user commands;
• hardware capabilities.

If competing AI assistants cannot access equivalent functionality, the operating-system provider can potentially reinforce its AI position through ecosystem control.

This is precisely why the Commission opened proceedings concerning Google's Android interoperability for competing AI services in January 2026.

The Commission subsequently adopted binding measures in July 2026 concerning interoperability with Android features relevant to competing AI services.

10. Behavioural Interoperability and Data

Interoperability increasingly overlaps with data access.

Examples include:

• portability of user data;
• access to platform-generated data;
• search-ranking data;
• click data;
• usage information;
• device data;
• transaction information.

The DMA separately addresses data portability and data access. The Commission has described Article 6(9) as requiring data portability for end users and Article 6(10) as addressing certain business-user data access.

Therefore:

Technical interoperability + data portability + data access

can collectively reduce ecosystem lock-in.

11. Interoperability and Self-Preferencing

A particularly significant problem occurs when a platform operates both:

1. the infrastructure; and
2. a competing downstream service.

For example:

Operating system → AI assistants

If the operating-system provider owns one AI assistant, it may have incentives to:

• provide its AI with privileged APIs;
• reserve certain device functions;
• delay competitors' access;
• restrict background operation;
• limit notification access;
• degrade third-party functionality.

An interoperability obligation attempts to prevent the infrastructure owner from using its control over the upstream layer to disadvantage downstream competitors.

12. Interoperability and Network Effects

Interoperability can weaken network effects.

Without interoperability:

More users → larger network → more developers → more complementary services → even more users.

This produces a reinforcing feedback loop.

With interoperability:

Users of Platform A ↔ users/services of Platform B

the competitive advantage associated with being inside the largest ecosystem may become less decisive.

This is particularly relevant to:

• messaging;
• social networks;
• payment systems;
• operating systems;
• cloud platforms;
• app stores;
• digital identity;
• financial APIs;
• connected devices.

13. Messaging Interoperability

Messaging interoperability is a distinct regulatory problem.

A user on Platform A may be unable to communicate with a user on Platform B because the platforms are technically closed.

The DMA contains a specific interoperability framework for certain number-independent interpersonal communications services under Article 7.

The regulatory rationale is that network effects can otherwise make switching difficult and strengthen incumbent platforms.

Importantly, the European Commission's 2026 DMA review stated that it considered it premature at that stage to extend the existing Article 7 interoperability requirements to online social networks.

This illustrates that interoperability obligations are not automatically appropriate for every digital market.

14. Limits on Behavioural Interoperability

Interoperability is not unlimited.

A dominant undertaking may have legitimate reasons to restrict access where necessary to protect:

A. Cybersecurity

Opening an API may expose security vulnerabilities.

B. Privacy

Interoperability may involve access to personal information.

C. System integrity

Third-party applications could interfere with the stability of an operating system.

D. Intellectual property

Technical disclosure may implicate patents, copyright or trade secrets.

E. Quality and performance

Poorly designed integrations can degrade system performance.

F. Consumer protection

Uncontrolled third-party access may facilitate fraud or misuse.

The DMA expressly allows gatekeepers to adopt measures that are strictly necessary and proportionate to protect the integrity of operating systems, hardware and software features, provided those measures are duly justified.

15. Proportionality

An effective interoperability obligation should generally answer five questions:

1. What functionality must be made interoperable?
2. Who is entitled to access it?
3. On what terms?
4. What security/privacy restrictions are legitimate?
5. How is compliance monitored?

An obligation that is excessively broad may undermine innovation.

An obligation that is excessively weak may merely create formal interoperability without meaningful competition.

16. FRAND and Interoperability

Where access is supplied commercially, competition authorities may examine whether conditions are:

• Fair
• Reasonable
• Non-discriminatory

FRAND principles can become relevant particularly where interoperability depends upon:

• technical standards;
• standard-essential patents;
• APIs;
• data access;
• communications infrastructure.

However, FRAND does not mean that every interoperability request must automatically be granted. The precise legal framework depends upon the applicable competition law, sectoral regulation and contractual/IP rights.

17. Interoperability as a Remedy

Competition authorities can design interoperability remedies around several dimensions.

18. Key Distinction: Access vs Effective Interoperability

This distinction is extremely important.

Mere access

"The competitor is technically allowed to connect."

Effective interoperability

"The competitor can connect and obtain functionality sufficiently equivalent to that available to the dominant undertaking's own service."

Modern digital competition regulation increasingly focuses on the second concept.

The Commission expressly describes the DMA obligation as requiring effective interoperability, rather than simply nominal access.

19. Competition-Law Test for Behavioural Interoperability

A useful analytical framework is:

Step 1 — Identify the market

Determine:

• relevant product/service market;
• geographic market;
• adjacent markets;
• platform/ecosystem relationships.

Step 2 — Identify market power

Examine:

• market share;
• network effects;
• switching costs;
• economies of scale;
• ecosystem control;
• entry barriers;
• data advantages.

Step 3 — Identify the bottleneck

Determine whether the undertaking controls:

• API;
• operating system;
• network;
• data;
• technical standard;
• app store;
• communications infrastructure;
• essential platform functionality.

Step 4 — Examine conduct

Look for:

• refusal;
• delay;
• discrimination;
• degradation;
• technical restrictions;
• self-preferencing;
• excessive access costs;
• contractual restrictions.

Step 5 — Establish competitive effects

Examine whether the conduct:

• forecloses competitors;
• raises rivals' costs;
• increases switching costs;
• protects the dominant firm's adjacent market;
• reduces innovation;
• limits consumer choice.

Step 6 — Consider justification

Assess:

• cybersecurity;
• privacy;
• intellectual property;
• technical integrity;
• proportionality;
• legitimate business justification.

Step 7 — Design remedy

Possible remedies include:

• API access;
• functional parity;
• technical disclosure;
• data portability;
• non-discrimination;
• monitoring;
• independent dispute resolution.

20. Comparative Case-Law Principles

21. Emerging Legal Trend

The jurisprudence shows an evolution:

Refusal to supply
↓
Essential facilities doctrine
↓
Interoperability information
↓
Technical access remedies
↓
API/data portability obligations
↓
Statutory interoperability duties for gatekeepers
↓
Technical specification and continuous compliance

The 2026 Google Android interoperability proceedings demonstrate the latest stage: competition regulation can become sufficiently technical that the regulator specifies how interoperability must actually operate, rather than simply ordering a company to "allow access."

22. Conclusion

Behavioural interoperability obligations are increasingly important instruments of modern competition law, particularly in digital markets characterised by network effects, ecosystems, switching costs and vertically integrated platforms.

The traditional competition-law approach, illustrated by Bronner and IMS Health, is cautious about imposing compulsory access because forced sharing can undermine investment and innovation.

The Microsoft cases demonstrate circumstances in which control over interoperability information can become an exclusionary competitive advantage.

Slovak Telekom shows the interaction between regulatory access obligations and competition law, while Google Android illustrates how control over a digital ecosystem can affect adjacent markets.

The modern regulatory approach represented by the DMA is more proactive. Instead of waiting for every interoperability problem to be litigated as a traditional refusal-to-deal case, designated gatekeepers can be subject to affirmative obligations concerning effective interoperability, data access, portability and non-discriminatory technical access. The EU's 2026 Android AI-interoperability measures demonstrate how these obligations are moving from broad legal principles toward detailed technical implementation.

The fundamental competition-law objective is therefore:

A firm controlling a critical technological interface should not be able to use that control to make downstream competition technically ineffective, while legitimate security, privacy, intellectual-property and innovation interests remain protected through proportionality and carefully designed access conditions.