The first stable compound produced from CO2 in the light-independent reactions (Calvin Cycle) is 3-phosphoglycerate (3-PGA).

Here's how it happens:

1. CO2 fixation: CO2 combines with a 5-carbon sugar called ribulose 1,5-bisphosphate (RuBP). This reaction is catalyzed by the enzyme RuBisCo.

2. Unstable intermediate: The product of this reaction is a 6-carbon compound that is very unstable and immediately breaks down into two molecules of 3-phosphoglycerate (3-PGA).

So, while CO2 is initially incorporated into RuBP, the first stable product is 3-PGA, which is then used to produce other sugars in the Calvin Cycle.