Bedrock Developer Beta

The Bedrock Developer Beta is a beta version of Bedrock Edition accessible only by developers and marketplace content creators. There hasn't been much documentation of the version.

Leak
The version was discovered and leaked by multiple sources, including a user known as TantalusC, and was showcased by a YouTuber known as Element X, alongside the 1.18 Developer Beta which included the unreleased fireflies and bundles. He received an email from Mojang Studios associates asking him to take down the video, threatening legal action against him, and the video was later taken down.

Notable Differences
This version has additional development features intended to aid developers, which include:
 * A debug screen similar to that in Java Edition.
 * The ability to enable on-screen touch screen controls to test them for mobile versions.
 * Advanced settings for terrain generation and weather.
 * A menu allowing for the modification of blocks, entities and particles in-game.
 * Creation of custom biomes.
 * A maximum framerate slider.
 * The ability to add free minecoins to the user’s account.
 * The ability to slow down time.
 * The ability to view hitboxes, mob info and AI pathfinding.
 * Various graphs.

Known Commands

 * aicreate
 * aigoals
 * aistop
 * audioaction
 * automate
 * bhave
 * bossbar
 * bounds
 * camera
 * changedimension
 * Likely changes the dimension you're in. (for example, going to the nether from the overworld)
 * cheat_ability
 * cheat_movement_debug
 * cleanroom
 * clearloadedstructures
 * corruptworld
 * crashclient
 * Likely causes an intentional client crash.
 * crashserver
 * Likely causes an intentional server crash.
 * debugcamera
 * debugprofile
 * destroyblock
 * dumpblocknames
 * dumpblockpalette
 * dumpentitiesclient
 * dumpentitiesserver
 * enchantrandom
 * equip
 * fillchestblock
 * filldrive
 * filllevelstorage
 * findanchoredbuildpos
 * findflatarea
 * findnearbypickup
 * fixbiomes
 * fly
 * Likely makes you fly.
 * getblockname
 * Likely shows a block's name.
 * getchestcontents
 * Likely shows a container's contents.
 * getdurability
 * Likely shows a tool's durability.
 * getexperience
 * Likely gives you a set amount of experience.
 * getmobdebuginfo
 * getpower
 * getselecteditemcount
 * getstructure
 * getworldname
 * health
 * hunger
 * insomnia
 * islargechestblock
 * isplayercrouching
 * isplayerflying
 * isplayergrounded
 * isworldloaded
 * kit
 * leaveworld
 * Likely removes the player from the world.
 * loadbehaviortreedefinitions
 * lookat
 * me
 * memwarn
 * mixer
 * This has likely been removed as Mixer no longer exists.
 * mobinfo
 * navigate
 * nearbyentityisbaby
 * notifyprofiler
 * option
 * particlelegacy
 * paths
 * pause
 * placefeature
 * placefromhand
 * placestructure
 * playerstat
 * postrackclient
 * postracksrv
 * profile
 * raid
 * record
 * redstonetest
 * register3pserver
 * reloadanims
 * restart
 * resupply
 * rot
 * savestructure
 * scheduler
 * selectinventoryitem
 * sendmodalform
 * sendshowstoreoffer
 * serverinfo
 * showallitems
 * showfrustum
 * simlock
 * simscale
 * skin
 * spawnfeature
 * spawngroup
 * spawning
 * spawnitem
 * spawnmob
 * Likely spawns any mob into the game.
 * spreadplayers
 * stest
 * stopsound
 * Likely mutes the game.
 * stoptime
 * Likely stops time.
 * systemstat
 * test
 * testassets
 * testfor
 * testforblock
 * testforblocks
 * timelock
 * title
 * titleraw
 * tpb
 * tptobiome
 * Likely functions like the locate command, but teleports you to the biome directly instead of giving you coordinates to it.
 * tptosuitabletree
 * transferserver
 * uidebug
 * videostream
 * videostreamaction
 * wipeout
 * wsserver