As with any Bethesda game launch, players have been waiting to star modding Fallout 4 since November. It seems that dream is closer than ever, as Bethesda is now answering requests to send out more invitations to the closed beta test for the Creation Kit. Players on the official Bethesda Forum just need to okay the non-disclosure agreement and will be considered for early access.
The Creation Kit is supposed to become available for players on PC sometime this month, with Xbox One following in May and PlayStation 4 shortly after that. This closed beta is only available on PC however, and invitation-only, so responding does not guarantee you access.