Boeing has said they have improved from 97% to 98% over the past 6 months and are equivalent to the 777 at the same stage, but they are striving to reach the current 777 99.7% readiness. The numbers seem incredible to me - I have not kept track of all the flights I have made when there was a mechanical delay but my estimate would be in the 90% - 95% range. In the 1980's our SAE (Society of Automotive Engineers - also covers aviation) chapter toured the TWA overhaul base in Kansas City. They had a chart listing the reliability rate of each airplane series. Lowest was the 747SP (I wasn't even aware TWA flew the 747SP) at 76% but none were over 95%. Maybe they are different measures - the TWA chart was for plane mechanically ready for an on-time departure.