In the alternate reality timeline, the Constitution-class was launched between 2255 and 2258, with the maiden voyage of the USS Enterprise in 2258, the launch perhaps having been delayed by Nero's temporal incursion.
The Constitution-class had a more militaristic design then that of its Prime universe counterpart, with phaser banks firing both multiple short burst rounds or steady beams along with torpedoes simultaneously in a barrage. The torpedo bay was located in the same position as the post-refit version from the original timeline, although only one torpedo bay is present firing a barrage of up to three torpedoes before re-arming. The phaser arrays are located on the dorsal and ventral sides of the saucer section and resemble the ball-turret style, also used in the post-refit version of the original timeline's class; firing red pulses (like proximity blasts), capable of continuous fire. (Star Trek)
The ship's dossier on the official movie website identifies the Enterprise as a Constitution-class heavy cruiser, the same as her prime universe counterpart, although this detail is not stated in the film. . The website also notes that she is being "held in Beta Testing Ward 956 - approved for combat". The maximum speed of the Enterprise is given as warp 8.
The bridge is located on A Deck and the sickbay on G Deck. The stated crew size is 1100. Enterprise Tour
The USS Enterprise for the new movie was designed by Ryan Church.
Despite structural similarities to the original movie Enterprise, multiple sources close to production provide varying, much larger measurements of the new ship:
The finalized length of the class is portrayed as 2379.75 feet (725.35 meters) in the Starships Blu-ray feature and Star Trek - The Art of the Film (see Note 4 in the book). Gizmodo blog writer Jesus Diaz was the first to reveal this number, citing as his source a "David B." of Bad Robot Productions. 
In a separate interview, Plant also asked Enterprise designer Ryan Church, who said that he was unable to address the changed size (compared to that of the original series Enterprise) and that ILM or J.J. Abrams could probably better answer the question. 
The article on the movie in Cinefex #118 notes that "the reconfigured ship was a larger vessel than previous manifestations — approximately 1,200-feet-long [370 meters] compared to the 947-foot ship [288.6 meters] of the original series". The statement is immediately followed by a quote from Visual Effects Art Director Alex Jaeger:
Once we got the ship built and started putting it in environments, it felt too small. The shuttle bay gave us a clear relative scale — shuttlecraft initially appeared much bigger than we had imagined — so we bumped up the Enterprise scale, which gave her a grander feel and allowed us to include more detail.
Star Trek illustrator John Eaves recalls that before he finished working on the movie in October 2007, the size of the Enterprise had been very much undefined, anywhere between 3000 and 5000 feet (900 and 1500 meters).  
A metric size chart dated September 10, 2007 shows the ship at 1200 meters in length (3900 feet), while some of the other vessels are also larger than in the later charts. (Star Trek - The Art of the Film)
In the Starships Blu-ray feature, Alex Jaeger is showing an ILM size chart dated January 14, 2008, with the Enterprise length at 2500 feet (760 meters). Earlier on his blog, Jaeger had quoted the same figure from an unspecified early chart, adding that the size may have been somewhat reduced later on. 
Other published size figures are summarized below:
- The length is stated as 2357 feet (718.4 meters) in a CG Society article on ILM's visual effects work for the film. 
- ILM model supervisor Bruce Holcomb said that the Enterprise is 2000 feet (600 meters) long in an interview for Studio Daily. 
- The Post Magazine article 'Star Trek' Returns gives a length of 3000 feet (900 meters). 
- Experience the Enterprise includes the following dimensions:
- Length: 2500 feet (760 meters)
- Saucer diameter: 1100 feet (340 meters)
- Height: 625 feet (190.5 meters)