What was the first Pokémon game to use 3D models for Pokémon?

Pocket Monsters Stadium was the first Pokémon game to use three-dimensional models for Pokémon.

Released in Japan for the Nintendo 64 in 1998, Pocket Monsters Stadium brought Pokémon battles into a 3D home-console environment. It was developed and published by Nintendo and featured battles, an announcer, and compatibility with the Game Boy Pokémon games through the Transfer Pak.

The game is easy to confuse with Pokémon Stadium. Outside Japan, the later and expanded title Pokémon Stadium was released as the first Stadium game in Western regions. The original Japanese Pocket Monsters Stadium was a separate, Japan-only release and supported only a limited selection of 40 Pokémon for battles.

Pokémon Stadium expanded the concept to all 151 species from Red, Blue, and Yellow. Much later, Pokémon X and Y became the first mainline games to use fully 3D graphics, but the Nintendo 64 Stadium experiments had already established 3D Pokémon battles years earlier.