If you haven't experienced Gambit for yourself and you want to know what all the fuss is about, you'll get your chance starting tomorrow.
It will be made available to all Destiny 2 players whether they own Forsaken or not. However, it's not yet clear whether free trial players will earn any rewards from the mode, or if their Infamy progress (Infamy being Gambit's dedicated progression system) will carry over should they purchase the Forsaken expansion afterwards.
At the beginning of each round, players will fight to capture a central zone. But that other team will be able to contest control of the zone while the team on the offensive is working to deploy the Breaker.
You can play on PC, PlayStation 4 and Xbox One and the only requirement is that you own the standard, base game of Destiny 2 and have it installed. Once the Breaker is captured, it will be used to assault and hack the enemy team's Vault.
When a team successfully hacks the enemy team's Vault, they win the round.
As of September 25, Breakthrough will pop up on the weekly featured playlist for a week, and then find a spot for itself in the competitive playlist. If you fail to hack the enemy team's Vault within the round time limit, you lose. The first team to win three round will be the match's victor.