Investors should put about 40 percent of their portfolios in non-U.S. stocks and bonds to diversify their holdings, according to top executives at Vanguard Group, the fund giant that manages $4.9 trillion.

Global stock markets are likely to outperform the U.S., which the firm expects to return roughly 4 percent to 6 percent annually over the coming decade, Chief Executive Officer Tim Buckley and Chief Investment Officer Greg Davis said Thursday during a webcast.

Vanguard formerly recommended allocating about 30 percent of portfolios to non-U.S. assets, the executives said. One reason for the increase: Fees have fallen on international funds, improving net returns.

Other comments from the Valley Forge, Pennsylvania-based firm:

• Expect volatility to continue in 2019. Last year was normal, while the low volatility of 2017 was an aberration.
• Stay invested. “Going all cash is way too risky,” Buckley said.
• Long-term U.S. Treasury yields are likely to rise as supply grows with an expanding deficit and foreign buyers diminish.
• The government shutdown is likely to slow U.S. growth by 0.1 percent or more per week.
• Competitors cut fees to zero on some funds as a marketing tactic, but Vanguard won’t go that low. “We’ll continue to do what we’re doing,” Buckley said.