RC6 is a significant performance tuning step for the most part. Code controlling floating-point exception handling has also been entirely reworked. The --enable-unicode option is now working again but is still off by default and remains experimental.

The performance difficulties were considered serious enough to postpone the completion of the 1.0.0 release process. There will be one last release candidate (7) before final release. It will complete the performance tuning, fix a few minor issues in slime and be a general opportunity to clean-up the source code.