From 1 January 2026, Australia will transition to a mandatory and suspensory merger control regime. In a series of articles, we have followed the progress of the reform package including the release of draft notification thresholds and the impact of the reform package passed by parliament. Australia is now entering the final stretch before the regime commences on a voluntary basis (from 1 July 2025) and then formally comes into effect in 2026. In these final few months, businesses and their advisers should expect a flurry of regulations and guidance materials from the ACCC.

In this update we briefly summarise:

• Updated draft merger review guidelines that address the ACCC's analytical approach to merger reviews.
• Recent guidance from the ACCC regarding transitional arrangements.
• FAQs released by the ACCC.
• What key details remain outstanding and when we can expect further information.

Updated merger assessment guidelines

In March 2025, the ACCC released draft updated merger assessment guidelines. They outline the analytical framework the ACCC will apply when assessing acquisitions notified under the new regime. Save for adjustments to reflect other legislative changes, the current ACCC merger guidelines have not been overhauled for over 15 years.

The draft updated merger assessment guidelines continue to address conventional matters including how the ACCC approaches market definition, and risks that arise in relation to horizontal, vertical and conglomerate transactions. There are, however, changes to ensure the guidelines address perceived emerging areas of concern and new 'theories of harm'. In particular, the draft guidelines address:

Features of the reform package that will impact the ACCC's analytical approach to reviews including:

• That a substantial lessening of competition (SLC) can include 'creating, strengthening or entrenching' a substantial degree of power in a market (significantly, so that even a small change in market power may amount to a SLC).
• That the ACCC may, in certain cases, be able to approach the effect of the notified acquisition as being the combined effect of the acquisition under review and certain previous acquisitions completed in the prior 3 years. This feature of the regime is directed at facilitating greater scrutiny of 'serial' or 'creeping' acquisitions.

Other issues that are increasingly the subject of scrutiny in the context of merger reviews including:

• Acquisitions that eliminate nascent or emerging competitors (so-called 'killer acquisitions').
• Transactions involving two (or multi-) sided platforms.

The ACCC's statement of goals for the merger reforms (released in October 2024) flagged a commitment to a risk-based approach with enhanced use of economic tools when assessing transactions. The draft merger assessment guidelines reflect this approach, including a greater focus on the potential use of economic tools such as diversion ratio analysis to assess the closeness of competition between merger parties.

The ACCC expects the guidelines to continue to be updated over time, to reflect decisions of the Australian Competition Tribunal as they occur.

Submissions on the draft guidelines will be accepted until 17 April 2025.

Further clarity regarding transitional arrangements

In March 2025 the ACCC also released further detail regarding transitional arrangements. These arrangements will be relevant to parties engaging with the ACCC now and before the mandatory regime commences in full in January 2026. It is critical that parties keep in mind that the incoming regime will apply to acquisitions that are 'put into effect' (ie which close) after 1 January 2026 – this means that the incoming regime will apply to many deals signed during the course of 2025.

Businesses and their advisers should be aware of the following transitional arrangements that the ACCC will apply:

Up to 30 June 2025:

• The current informal merger clearance process and the formal merger authorisation regime (which is rarely used) will continue to operate.
• Where an informal pre-assessment is finalised before 1 July 2025 but the acquisition will not be put into effect by 31 December 2025, parties will need to consider re-engaging with the ACCC to seek updated or 'refreshed' informal review. The ability to approach the ACCC to 'refresh' a prior clearance can occur from 1 July 2025.

From 1 July 2025 to 31 December 2025:

• Merger authorisation applications can no longer be submitted. Applications for formal merger authorisation (if any) submitted prior to 1 July 2025 will continue to be assessed up until 31 December 2025.
• Informal clearance applications (or requests for an updated informal review) should be submitted as early as possible to mitigate the risk of the review not being completed by 31 December 2025. The ACCC has indicated that anything submitted 'after early October… [is] much less likely to be considered in time', even where limited or no competition risks arise. Where informal clearance is granted in this period, parties have 12 months to put the acquisition into effect (if that does not occur, then notification under the new regime will be required).
• Voluntary notification under the new formal regime becomes available.
• The ACCC will cease reviewing applications (informal or merger authorisation) after 31 December 2025.

From 1 January 2026:

• Where an acquisition that meets the notification thresholds has not been cleared (formally or informally) as at 1 January 2026, it will need to be (re)notified and assessed under the new regime. While the ACCC may adopt a truncated review to reflect work already done, it has not clarified how this will operate in practice.
• Where an acquisition does not meet the notification thresholds there is no requirement to notify, although there may be residual risk under Australian competition law as the ACCC will retain the ability to investigate and take enforcement action against any merger that is not notified where it is likely to SLC in a market.

Key takeaways for business and advisers

Business and their advisers who are preparing for the merger reforms need to be particularly mindful of the following:

1. Despite the objectives of the regime including faster decisions, greater transparency, clearer notification pathways and streamlined processes, businesses should expect turbulence and potential delay during the transition period and the early stages of the new regime. The ACCC has committed to greater certainty and quicker decisions for merger parties. Whether that is achieved is now primarily in the hands of the ACCC and its staff.
2. While the current informal merger clearance regime will remain in place until 31 December 2025, the ACCC has effectively set an October 2025 deadline for applications under the current regime. In H2 2025 there will be an increasing focus on strategic decisions regarding filing and filing pathways. Businesses should prepare for this.
3. The ACCC has flagged that reviews that are ongoing at 31 December 2025 will result in 'no decision' and will need to be notified under the new regime. While a tailored approach may be adopted for in-flight reviews, the message from the ACCC is – leave ample time for a review to be completed, or file (voluntarily) under the new regime.
4. Merger parties who have already signed transactions will need to monitor for any changes in the expected completion date. If there is a risk that completion may be pushed out into 2026, steps should be taken (early) to seek a 'refreshed' decision from the ACCC, or consider the notification thresholds under the incoming regime.
5. For transactions being negotiated at present, parties need to consider appropriate conditions precedent to account for the new regime, including optionality that may be required depending on the timing for completion.
6. Any ACCC decisions from 1 July to 31 December 2025 under the current informal clearance regime should provide protection under the new regime, provided that completion occurs within 12 months of the ACCC's decision. However, no protection will arise for decisions that are brought to the ACCC's attention only via a FIRB application.

FAQ

The ACCC has also released 'Frequently Asked Questions' guidance on the merger reform transition, which supplements the general information on the ACCC’s website. The FAQs include some of the 'initial' questions the ACCC is being asked. The ACCC has flagged the FAQs reflect their early views only and may be amended from time to time to reflect experiences during the transaction.

While the FAQs cover a range of matters, they notably confirm:

• The ACCC will have a tailored approach to information which is required upfront and will provide guidance for when a 'simpler or longer notification form' may be appropriate.
• The ACCC values 'robust engagement' with parties and has an 'incentive to disclose sufficient detail to enable it to test material issues with the parties';
• The ACCC plans to approve around 80% of acquisitions in 15 to 20 Business Days via an early Phase 1 determination or the notification waiver process;
• The public register will not include submissions from the parties, or third parties.

Some key details remain outstanding

Despite the 1 July 2025 transitional period rapidly approaching, some material details about the regime remain outstanding. This includes:
Critical ACCC guidance about the incoming merger process which we expect to be released in the coming week. This will need to include additional supporting material such as application forms setting out the information / details of documents to be provided to the ACCC, and detailed information about the waiver notification process.

Applicable notification thresholds have not yet been finalised – while some detail has been provided by Treasury, key details regarding the scope of the thresholds will need to be formalised through regulations.

Other matters also need to be addressed via regulations including filing fees (Treasury has indicated they will be in the range of A$50,000 to $100,000 with exemptions in certain cases), and details about the public register.