Beta 184.108.40.206 (Bedrock beta version numbers start at 50 for some reason) adds all of the features unique to Caves & Cliffs Part One.
The lush caves biome, filled with a variety of plants, now generates underground, filled with dirt, glay and moss.
New blocks added in this beta include all varieties of amethyst, raw metal blocks, tuff and calcite rocks, and tinted glass.
New items include item forms of the raw metals and the spyglass, including a unique animation for looking through one.
This beta also brings other features from Java Edition to bring update parity between the two editions, including copper being oxidised when struck by lightning as well as stalagmite growth.
The beta is available on Xbox One, Windows 10, and Android for users who have entered the beta program on each platform's respective store. The "Experimental Gameplay" toggle must be enabled before creating a world in order to receive the new Caves & Cliffs content.