Microsoft Advertising makes optimization experiments generally available

Microsoft Advertising said on 30 September 2026 that optimization experiments are now generally available for Search, Shopping, Audience and Performance Max campaigns, in its monthly product update on the Microsoft Advertising blog. The same post announced a Microsoft Advertising integration inside HubSpot, raised the LinkedIn company list limit from 1,000 to 10,000 company names, and changed the plan for its SOAP to REST API move while keeping SOAP's 31 January 2027 shutdown date.

The four September 2026 updates at a glance

Microsoft framed the September post, titled "Less busywork, more growth", around the run-up to the holiday season. The table below lists each announcement as Microsoft described it.

Optimization experiments are now generally available

The biggest change for day-to-day account management is testing. Microsoft Advertising said optimization experiments are now generally available for Search, Shopping, Audience and Performance Max campaigns. Advertisers can run controlled A/B tests on bidding, targeting, creative "and more" to see how a change affects performance before rolling it out.

Microsoft described three parts of the workflow:

• A controlled A/B test of a change against the current campaign setup.
• A unified results page that compares the experiment with the original setup side by side.
• When a change wins, it can be applied to the original campaign or used to create a new campaign.

Microsoft also gave its own reason for the timing. With the holidays ahead, it said, now is a good time to test and lock in what works, so campaigns have time to build a stable baseline before demand peaks. That is Microsoft's advice, but the logic is sound for any advertiser: a test started in late November has little room to finish before the busiest weeks.

The blog post points to a help resource called "Experiment with your campaigns" for setup details. The post itself does not give traffic or budget split options, minimum test durations, or the statistical significance threshold used to call a winner. Anyone planning a test should check those in the help documentation inside their account rather than assume they match Google Ads.

Why Performance Max testing matters

Performance Max is the campaign type where controlled testing is hardest, because so much of it is automated. Without a native experiment, advertisers typically change a setting and compare before and after periods, which mixes the effect of the change with seasonality, competitor activity and budget shifts. A split test inside the platform separates those effects. For advertisers running Performance Max on Microsoft Advertising, general availability means this kind of test is now a standard option for that campaign type.

Microsoft Advertising is now live in HubSpot

Microsoft called the HubSpot integration "this month's top story". According to the 30 September post, advertisers can connect Microsoft Advertising inside HubSpot and use it in three ways.

Audiences from CRM data. Advertisers can use HubSpot contacts to reach audiences in Microsoft Advertising. Microsoft said this includes verified LinkedIn professionals across Bing, Copilot, Outlook, Xbox and more, and that advertisers can engage and retarget prospects and customers across the Microsoft ecosystem.

Automated lead follow-up. When a Microsoft Advertising campaign captures a new lead, it can automatically trigger a next best action set up in HubSpot. Microsoft's examples were assigning a sales representative or sending a nurture email.

Pipeline and revenue reporting. By connecting ad clicks to the contacts and deals tracked in HubSpot, advertisers can see which ads drive pipeline and revenue, and compare performance across channels side by side.

Microsoft said requirements, including eligible subscription plans, access levels and setup guidance, are covered in a HubSpot knowledge base article. The blog post itself does not list which HubSpot plans qualify, so B2B teams should confirm eligibility before planning around it.

For lead-generation advertisers, the reporting part is the most useful. Platform-reported conversions stop at the form fill. Matching clicks to deals in a CRM shows which campaigns produce revenue, which is the number that should guide budget. That kind of closed-loop reporting depends on clean tracking and CRM data, the same groundwork that sits behind good analytics and conversion measurement.

LinkedIn company lists now hold 10,000 companies

Microsoft Advertising raised the limit on LinkedIn company lists to 10,000 company names per list, up from 1,000. Advertisers can add the companies all at once during campaign setup or in the audience library, instead of entering them one at a time, and then use the lists with LinkedIn profile targeting in Search and Audience campaigns.

Microsoft's own example is a B2B software company that wants more demo requests from 8,000 target accounts. Under the new limit, all 8,000 fit in one list, and the demo offer can be shown to people who work at those companies across Search and Audience campaigns.

Three conditions in the post are worth noting:

• LinkedIn company lists are available to advertisers globally in supported markets.
• Company names are displayed mostly in English.
• The underlying consumer data excludes users in the EEA, the UK and Switzerland.

The English-names point matters for advertisers whose target accounts are often known by local-language names. Matching a target list to the names Microsoft displays may take some cleaning before upload. The EEA, UK and Switzerland exclusion means account-based campaigns aimed at European buyers will not reach users there through this targeting.

SOAP to REST: more time for new features, same deadline

The fourth update is for anyone who manages Microsoft Advertising through the API, including in-house tools, bid management platforms and reporting pipelines. Microsoft announced the move from its SOAP API to a REST API in April 2026. It had planned to make new features and enhancements REST-only starting 1 October 2026.

Based on advertiser feedback, Microsoft said on 30 September that it is extending that timeline:

• New features and enhancements will be available in both SOAP and REST until SOAP is deprecated on 31 January 2027.
• The SOAP API will still be fully deprecated on 31 January 2027.

In other words, the feature freeze on SOAP moved, but the shutdown did not. Teams still on SOAP now get new features for about four more months, and they still have until 31 January 2027 to finish the migration. Microsoft pointed SDK users to its SDK migration documentation, and told non-SDK users to update their implementation to REST API URLs and request formats. It also suggested that teams not yet using an SDK consider switching as part of the migration. For complex integrations that need more time, Microsoft said advertisers can contact their account team or Microsoft Advertising support to discuss an extended migration plan.

The practical risk is easy to miss: any script, connector or third-party tool that still calls SOAP will stop working after 31 January 2027 unless it is moved. Agencies and in-house teams should list every integration that touches the Microsoft Advertising API and confirm with each vendor which API it uses.

What Microsoft did not say

The September post is short on mechanics in a few places. It does not give:

• Traffic or budget split ratios, minimum durations, or significance thresholds for optimization experiments.
• The specific HubSpot subscription plans that qualify for the integration (Microsoft refers readers to HubSpot's documentation).
• A list of which markets count as "supported markets" for LinkedIn company lists.
• Any change to the 31 January 2027 SOAP shutdown date, which it explicitly kept.

Where these details matter to a decision, check the in-product help or ask a Microsoft account team instead of relying on summaries.

What this means for Thai marketers

For Thai advertisers, the value of these updates depends on who they sell to. Thai exporters, hotel groups and B2B firms that use Microsoft Advertising to reach buyers in the US, Australia or other English-speaking markets can use optimization experiments to test Performance Max and Shopping changes before the year-end peak, rather than editing live campaigns and hoping. B2B companies with account lists of several thousand targets can now fit them into a single LinkedIn company list, provided their target accounts are outside the EEA, the UK and Switzerland. For Thai businesses selling mainly to Thai consumers, Microsoft Advertising is usually a smaller part of the media plan, and these updates change little.

The REST migration applies everywhere. Any Thai agency or brand that pulls Microsoft Advertising data into dashboards, or pushes bids and budgets through scripts, needs to confirm its tools are on REST before 31 January 2027. Running paid search across more than one engine, with consistent testing and measurement, is part of how paid search management should work in 2026.

Frequently asked questions

Which Microsoft Advertising campaigns support optimization experiments?

Search, Shopping, Audience and Performance Max campaigns, according to Microsoft Advertising's 30 September 2026 blog post, which said experiments are now generally available for all four. Advertisers can test bidding, targeting, creative and other settings.

When does the Microsoft Advertising SOAP API stop working?

Microsoft said the SOAP API will be fully deprecated on 31 January 2027. The date did not change; what changed is that new features will keep arriving in both SOAP and REST until then, instead of becoming REST-only from 1 October 2026.

How many companies can a LinkedIn company list hold in Microsoft Advertising?

Up to 10,000 company names per list, up from 1,000. The lists work with LinkedIn profile targeting in Search and Audience campaigns, and the underlying data excludes users in the EEA, the UK and Switzerland.

Does the HubSpot integration cost extra or require a specific HubSpot plan?

The blog post did not say. Microsoft said requirements, including eligible subscription plans and access levels, are covered in HubSpot's knowledge base, so check there before planning around the integration.

Is this available to advertisers in Thailand?

Microsoft did not name Thailand. It said LinkedIn company lists are available globally in supported markets, and it did not give market restrictions for optimization experiments or the HubSpot integration, so confirm availability inside your account.

Next steps

With experiments now generally available and the SOAP deadline fixed at 31 January 2027, the two jobs for Microsoft Advertising users this quarter are clear: start any holiday tests early enough to finish, and confirm every API integration is moving to REST. If you want help running structured tests across Google Ads and Microsoft Advertising, Relevant Audience manages search advertising campaigns for brands in Thailand and the region.