What has changed is that the United States are no longer a part of it.
The new agreement (now renamed Comprehensive and Progressive Agreement for Trans-Pacific Partnership, in short CPTPP) is between all the other parties which were pursuing the agreement:
- New Zealand
- (United Kingdom is "showing interest")
Details about the content of such trade agreements are hard to come by, because they are usually not presented to the general public until they are signed. Also, the negotiations about the CPTPP have just begun.
But we can assume that the United States, as the largest economy in that partnership, put quite a lot of their handwriting into the TPP contract drafts. With the US out of the picture, any clauses which the US would have never agreed to can be reconsidered and any clauses the US insisted on can be removed. So it makes sense to start from scratch and renegotiate the whole agreement.