Greg Abel completed his first 100 days as CEO of Berkshire Hathaway. He is implementing a proactive management style that scrutinizes the conglomerate's portfolio.

Abel expects higher performance from underperforming assets than his predecessor, Warren Buffett. The company restarted its share buyback program and increased investments in Japan.

Abel designated Apple and American Express as core holdings in his first shareholder letter. He signaled that positions in Bank of America and Chevron may not share that status.

Investors are monitoring how Abel will deploy Berkshire Hathaway's massive cash reserves during this new era.