Earlier this week, Tribes: Ascend studio Hi-Rez announced it was adding a single purchase option to

its free-to-play multiplayer shooter -- although the reasoning behind this was left unknown. As you'd expect, this led to much speculation regarding whether the free-to-play model was working out for Tribes , or whether the new payment option is being included to combat declining free-to-play sales.

Why did free-to-play Tribes Ascend add a buy-to-play option?

Gamasutra put the question to Hi-Rez COO Todd Harris: Is this new payment option a means to pull in those players who may have been put off the fact that the game is free-to-play, or is it a response to how the game has been selling as a free-to-play title?

"The first," he answers. "There are some people who are still put off by free-to-play, or fear a long grind will be required to access enough weapons, or fear pay-to-win. We wanted to remove any and all of those perception issues."

As for the game's in-game item sales, Harris tells us that the game is "selling as expected." (Within a month of launching as a free-to-play title last April, the game had been downloaded 1.2 million times. More recent numbers are under wraps.)

"In general for free-to-play downloadable titles, you tend to see around 10 percent of players choosing to purchase in-game items with real money transactions," he adds, "and Tribes Ascend is in that same ballpark."

Tribes Ascend was released last April, meaning that Harris now has a much better idea of how free-to-play works with triple-A multiplayer shooters -- and he's still very happy that his studio went with the model.

"Thanks to free-to-play, Tribes: Ascend reached a much larger audience than all previous four Tribes games combined," he notes. "So it has treated Tribes well.

"That said, we think additional payment options could support even further growth," he adds.

And Harris suggests that studios currently in the midst of building a multiplayer online game should definitely head down the digital download route, rather than wasting time with retail.

"The digital distribution model allows a studio to communicate directly with players and also to update the game more frequently," he explains. " Tribes Ascend has certainly improved over time thanks to community input. We recommend giving the player choices around how to pay -- and free is still a popular choice."