If you need a code check the link listed on Halo Infinite’s news and events!
Took me a few tries but I started from the bottom going up and I believe my code used was B41K-YGGM-6MXF-Z2SG-WJ4Y so anything above that I hope is still free for you.
Worked for me. Already tested the Xbox build and was fun. Hopefully test the PC build with this code since oddly 343i only let me test the Xbox build.
The funny thing Is, I signed up for the pc beta but was sent an invite to the Xbox version, which seems to have happened to a lot of people, so I decided to try one of the codes on the Steam post that you linked and this one worked.
53JV-PJVR-YGMF-IPSC-JGAU
By the way, I started from the bottom and worked up so all of the ones below that one have been used the max number of times.