In-Universe:
The U.S.S. Defiant approaches a mysterious planet in the Gamma Quadrant that is encased in a energy barrier.
Production:
Reasons for being CGI:
The opening scene shows the Defiant get pretty small as it get's closer to the planet. I'm not sure if they could pull the camera that far away on a motion control dolly.
Reasons for being Studio Model:
If you look at the 8 circular plasma vents on the Defiant, they are magenta in color, not blue/white like they should be. This can been seen here and also in the final scene as well. I think this may be evidence for being the studio model because Gary Hutzel created an amazing scene of the studio model for the Ships of the Line Calendar (year???) and the plasma vents are the same magenta color! It's possible there was a lighting issue inside the studio model around that time and that's why the color changed.
