A blog post by Victor Hugo Delfante Borborema
Can a digital platform exercise significant market power when its users regularly use competing services?
This question lies at the heart of Bytedance v Commission (C-627/24 P), the first dispute concerning the Digital Markets Act (DMA) to reach the Court of Justice of the European Union.
On 15 October 2026, Advocate General Andrea Biondi delivered his Opinion, recommending that the Court reject key arguments advanced by ByteDance against TikTok’s designation as a gatekeeper.
Central to the dispute is multi-homing: the practice of using several competing platforms simultaneously. ByteDance argued that this behaviour demonstrated TikTok’s exposure to competition.
The case raises a broader question: does the availability of alternative platforms necessarily prevent one platform from becoming an important gateway to consumers?
The legal framework: When does a platform become a gatekeeper?
The Digital Markets Act seeks to promote fairness and contestability in digital markets through obligations imposed on designated gatekeepers.
Unlike Article 102 TFEU, the DMA does not require a finding of dominance or unlawful conduct before its obligations apply.
Under Article 3(1) DMA, an undertaking qualifies as a gatekeeper where three cumulative conditions are satisfied: it has a significant impact on the internal market; provides a core platform service constituting an important gateway between business users and end users; and enjoys, or is expected to enjoy, an entrenched and durable position.
Article 3(2) establishes quantitative thresholds that create rebuttable presumptions. For the important-gateway requirement, these include at least 45 million monthly active EU end users and 10,000 yearly active EU business users.
Under Article 3(5), undertakings may challenge those presumptions through sufficiently substantiated arguments. The crucial issue is therefore not simply whether a platform meets numerical thresholds, but what evidence is necessary to challenge the conclusions drawn from them.[1]
TikTok’s challenge: Does multi-homing weaken gateway power?
In September 2023, the Commission designated ByteDance as a gatekeeper in respect of TikTok, which it classified as an online social networking service. ByteDance challenged the decision, arguing, among other things, that widespread multi-homing undermined the conclusion that TikTok constituted an important gateway.[2]
The General Court rejected the action in July 2024.[3]
ByteDance’s argument reflects an intuitive understanding of competition: when consumers can easily access alternative services, individual platforms should face stronger competitive constraints.
However, the relationship between multi-homing and market power is more complicated.
Consider someone who maintains accounts on TikTok, Instagram and YouTube but spends most of their time on TikTok. Although this individual technically uses three platforms, their attention is not distributed equally.
For an advertiser seeking to reach that individual, the availability of other social networks may therefore offer only limited substitutability.
This distinction between access to alternatives and their effective competitive significance is central to the Advocate General’s reasoning.
In paragraphs 77–103 of his Opinion, Biondi explains that multi-homing may be relevant to assessing gateway power, but does not automatically establish the absence of network effects or user lock-in.
Importantly, Article 3(1)(b) requires a platform to constitute an important gateway, not the only gateway through which businesses can reach consumers.[4]
Market power without exclusivity
The economic literature reinforces this distinction.
Belleflamme and Peitz demonstrate that multi-homing can coexist with competitive bottlenecks in two-sided markets, although its effects depend on the market structure.[5]
This insight matters because digital platforms connect different groups whose interests are interdependent. Consumers may participate in several networks while businesses remain economically dependent on access to particular audiences.
TikTok illustrates the problem. Even where users maintain competing accounts, a platform may retain distinctive advantages through engagement, network effects or access to particular demographic groups.
Consequently, the absence of exclusivity does not necessarily imply effective contestability.
The relevant question is not merely whether users can access competing platforms, but whether those alternatives meaningfully constrain the platform’s commercial importance.
Rebutting the presumption: How much evidence is enough?
A second significant issue concerns the evidentiary standard under Article 3(5) DMA.
Advocate General Biondi considers that rebutting a gatekeeper presumption requires a high degree of plausibility. Mere doubts or preliminary evidence are insufficient.
However, an undertaking need not conclusively disprove its gatekeeper status simply to obtain further examination.
Where sufficiently substantiated arguments manifestly call the presumption into question, the Commission must undertake a market investigation if it wishes to pursue designation, unless the qualitative requirements are already demonstrably absent.[4]
This interpretation balances administrative efficiency against procedural protection, while preserving a demanding threshold for challenging designation.
Nevertheless, the practical consequences deserve scrutiny. If extensive multi-homing is treated as insufficient without additional evidence, undertakings may face considerable difficulties demonstrating that their services remain contestable.
The answer should not be to treat multi-homing as irrelevant. Rather, regulators should examine its economic significance through evidence of engagement intensity, switching behaviour, audience overlap and business-user dependency.
These are proposed analytical considerations, not additional statutory requirements.
The broader tension: Effective regulation and meaningful scrutiny
The Opinion also examines procedural fairness.
Biondi argues that, in a presumption-based designation procedure, Article 41(2)(a) of the Charter does not generally require the Commission to disclose its provisional evaluation of evidence before adopting its decision. It must nevertheless examine the undertaking’s submissions carefully and impartially and provide adequate reasons.[4]
The resulting framework prioritises rapid regulatory intervention while retaining opportunities for rebuttal and judicial review.
Its effectiveness will depend on whether those opportunities remain meaningful in practice.
Conclusion
Bytedance v Commission exposes a central difficulty in regulating digital markets: consumer choice and market contestability are related, but they are not interchangeable.
Multi-homing may reduce switching barriers and facilitate competition. Yet it does not necessarily prevent platforms from acquiring significant commercial influence over access to consumers.
The Advocate General’s Opinion therefore supports an understanding of gateway power that looks beyond the mere availability of alternative services. What matters is whether those alternatives provide effective competitive constraints.
At the same time, the DMA’s presumption-based designation mechanism raises legitimate questions about evidentiary burdens and procedural safeguards.
As the Court of Justice considers the appeal, the broader challenge remains: how can EU digital regulation identify durable gateway power without treating platform size and popularity as conclusive evidence of market power?
References
[1] European Parliament and Council, Regulation (EU) 2022/1925 on contestable and fair markets in the digital sector (Digital Markets Act) [2022] OJ L265/1, arts 3(1), 3(2), 3(5), 3(8) and 17(3), recitals 13 and 23.
[2] European Commission, ‘Summary of Commission Decision of 5 September 2023 relating to Case DMA.100040 – ByteDance – Online Social Networking Service’ (2023) OJ C/2023/552. See also European Commission, ‘Digital Markets Act: Commission designates six gatekeepers’ (Press Release, 6 September 2023).
[3] Case T-1077/23 Bytedance Ltd v European Commission EU:T:2024:478, paras 174-214.
[4] Case C-627/24 P Bytedance Ltd v European Commission, Opinion of AG Biondi, 15 October 2026, EU:C:2026:861, particularly paras 22–36, 77–103 and 142–184.
[5] Paul Belleflamme and Martin Peitz, ‘Platform Competition: Who Benefits from Multihoming?’ (2019) 64 International Journal of Industrial Organization 1–26.
[6] Alba Ribera Martínez, ‘The Requisite Legal Standard of the Digital Markets Act’s Designation Process’ (2024) 20(4) Journal of Competition Law & Economics 265–291, especially 286 (as referenced in AG Biondi's Opinion, footnote 11).
[7] Court of Justice of the European Union, ‘Advocate General Biondi: the Court should dismiss the action brought by Bytedance (TikTok) against the decision of the Commission designating it as a gatekeeper under the Digital Markets Act’ (Press Release No 151/26, 15 October 2026).