Popular enterprise messaging platform Slack has announced it will be increasing the price of its Pro plan for the first time, while also making significant changes to its Free plan.

From September 1, monthly Pro subscriptions will increase 9%, from$8 to$8.75 per user, per month, and annual Pro subscriptions will increase 8%, from$6.67 to$7.25 per user, per month.

Customers wanting to remain on the existing annual Pro price of$6.67 a month for another year can do so by renewing an existing annual plan before September 1, or by upgrading a monthly Pro plan to an annual plan before the same date.

Companies currently on Slack's$12.50 per month Business Plus, or custom enterprise plans will not be affected by the price increases.

What's changing for Free users?

Changes to Slack's free offering will also come into effect from September 1.

Currently, users of the free plan have a 10,000-message limit and 5GB of file storage. Moving forward, free users will instead have full access to their message history and file storage for the past 90 days.

There will also be expanded access to premium features such as 'Clips', a video and audio messaging tool that lets users send short recordings to colleagues via direct messages or into channels. Free teams can also now set a custom retention period for their messages and files.

In a blog post outlining the changes, Slack said that the price increases reflect the value that has been added to the platform since it was first launched in 2014 and helps to "ensure that [Slack] can keep investing in innovation."