Solo authorship represented 80 percent of economics papers in 1960 and 65 percent in 1990, but then solo-authorship fell out of the majority in 2005 and represents only 26 percent of economics papers today (as measured by the right-hand axis). To put it another way, in 1950, there were 1.2 authors per economics paper. Average team size reached 2.0 for the first time in 2010. By 2018, team size averaged 2.7 (as shown on the left-hand axis). The jump in average team size in economics papers over the last ten years is greater than the jump over the prior half-century.

Here is more from Benjamin F. Jones.  For higher impact papers, the trend is even more striking.