This division has the greatest authority - Panini - behind it. In his Ashtadhyayi - he sees two languages - the language of Chandas and just plain "bhasha" the spoken language of his time.
Chandas approximately refers to older, metrical scriptures like Rig Veda.
Classical Sanskrit refers to the language codified by Panini, after excluding ...
Vedic sanskrit is different from classical sanskrit. Because vedic sanskrit was used around 1500 to 600bce and vedas were written in vedic sanskrit.
After that classical sanskrit was used.
There are major and minor differences in the pronunciation and spelling of words(same words) and vocabulary is also different .
Understand it with this example :
Rig Veda ...