The test runs until August 1st.
Image: 343 Industries

The network campaign co-op test flight is live. You will be able to play the campaign with up to three of your friends as part of the test. The game didn't include a mission replay feature when it was launched.

You should be aware that you will be starting the campaign from scratch in this test. The retail build of the game won't carry over any progress you've made in the test and the test won't show up in the retail build either. If you haven't played through the campaign in a while, starting fresh with your friends could be a good way to get back into it.

The developer has a dedicated support page for the flight on its website, as well as detailing what you can expect in the test in an extensive post. If you receive an invite, you will be able to try the test on steam.

The test was supposed to be launched the week of July 11th, but it is still a bit late. On August 1st, the test ends. We don't know when campaign co-op or mission replay will be released, but 343 Industries says it will be in August. The timing for split-screen co-op was listed on the road map as TBR.

Related

Halo Infinite campaign review: playing the hits