Salesforce and Slack are expected to announce a sales agreement Tuesday, in what would be Salesforce’s biggest acquisition to date.

The two companies made headlines Wednesday with news that Salesforce was looking to purchase the iconic corporate messaging app. At the time, talks were thought to still be in the preliminary stages, with no indication a deal was in sight. Within hours, however, outlets starting reporting the talks were in the advanced stages.

Things have progressed quickly, as a new report from the Wall Street Journal says a deal could be announced as early as Tuesday after market close. CNBC’s David Faber reports the deal will be roughly half cash and half stock, although it may be slightly weighted toward the cash side.

Similarly, while initial reports valued Slack at $17 billion, it appears Salesforce will be paying a significant premium. Faber said the deal is not expected to reach $30 billion, but may come close.

Experts believe the acquisition will help Slack, as well as Salesforce, fend off Microsoft. Slack has been hurt by a number of factors, most significantly Microsoft’s bundling of Teams with Office. Microsoft’s tactics prompted Slack to file an antitrust claim with the EU, a claim Jim Cramer calls “strong.”

At the same time, Microsoft continues to go after Salesforce’s core CRM market. Its most recent inroad was a partnership with C3.ai and Adobe to create AI-driven CRM.

The combination of the two companies may ultimately help both compete with Microsoft more effectively.