Today marks four years since Hubway launched in Boston, and the bike sharing system is celebrating with a massive expansion.

Hubway has 139 stations, but the officials said they plan to add 20 more throughout Boston and Cambridge during the next half of the 2015 season.  

Hubway Spokesman Benjy Kantor told Metro that while the locations of the new stations have not been determined yet, “there will be hub-bub surrounding the extension later in the season,” so bikers should stay tuned.

Kantor told Metro that they weren’t hosting a big celebration for their anniversary because of the extension plans and the buzz that will surround that later this year. However, Hubway officials will plan a collaborative special or celebration within the cities that Hubway resides, he said.

Cyclists may also be looking at new lighter, sleeker bikes, but Kantor said the cities have yet to confirm the upgrade.

Since 2011, Hubway users have offset more than 3 million tons of carbon, the system reported. Bikers can also be collaboratively proud of themselves for burning almost 200 million calories in the past four years.

The website offers an ongoing statistics list on their website along with ways bikers can track their own usage. To join the movement or for more information visit http://www.thehubway.com/home