[WP8Expert]

If all goes well, WP8.1 will be announced at MWC2014. MS will announce the WP8.1 update after Nokia finishes rolling out the black update, same as when GDR3 was announced after the Amber update completed stage 1 of its rollout.

GDR2 was announced after the Portico rollout was completed. GDR3 was announced after the initial Amber rollout begun. The Black rollout has begun so WP8.1 (Blue) will be announced VERY soon.

[12Danny123]

I think more of a sneak peak of WP8.1 and more to be announced at Build 2014

[N_LaRUE]

Source? From all information we've received so far WP8.1 is to be released in April at their BUILD event. That's the timeline that I've heard.