Global M&A deal volume reached nearly $4 trillion in 2018—a hot year for the most lucrative practice at elite law firms. For two of those firms, Wachtell, Lipton, Rosen & Katz and Cravath, Swaine & Moore, the boom pushed profits per equity partner to new heights—$6.53 million at Wachtell and $4.62 million at Cravath.

Wachtell and Cravath remain small compared with their mega firm competitors, helping them boost profits even more. Wachtell, with 267 attorneys last year, and Cravath, with 519, each operate largely from a single office, setting them apart from the other Am Law 100 regulars in the M&A league tables.

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Other key traits have become part of their legacies, defined their brands and perhaps fed into their success: They each have a one-tier partnership; they rarely hire laterals (and when they do, it's not to gain a book of business); and they utilize a traditional lockstep compensation model to pay partners by seniority.

Wachtell and Cravath have retained their twinned models amid increasing competition with global firms, which are betting on scale and lateral hires to gain more market share—often with stunning success. In the last decade, firms with competing M&A practices have approached or sailed past 2,000 attorneys. Several of these competitors are growing their presence outside the United States, offering a one-stop-shop model for global clients.