Several chests on Apex are opened with keys rather than found open. Each one has its own key, its own source, and its own reward table.

Brimstone chest

Opened with	Larran's key
Key source	Wilderness activity
Cost per open	One key, unless saved

You need a key in your inventory to open it. Without one you are told so and nothing happens.

Saving your key

Supporter rank gives a chance to keep the key when you open the chest. When it triggers you get a message:

Your donator status allows you to save your key!

Rank	Chance to keep the key
No rank	None
Bronze Supporter	2%
Iron Supporter	5%
Gold Supporter	8%
Mithril Supporter	10%
Adamant Supporter	12%
Rune Supporter	15%
Dragon Supporter	18%
Supreme Donator	20%

At Supreme Donator that is one free open in five, which meaningfully changes how far a stack of keys goes.

Slayer key chest

Slayer keys come in four tiers, and which tier you receive depends on the slayer master who set your task.

Key tier	Masters that award it
Tier 1	Turael, Mazchna, Vannaka
Tier 2	Chaeldar, Nieve, Konar
Tier 3	Duradel, Krystilia
Tier 4	Nomad, the boss master

Higher tier keys open better reward tables, which is a second reason to move up to a higher master beyond the points. Krystilia and Duradel both give tier 3 keys, and only the boss master gives tier 4.

Tier 1 slayer keys can also be bought from the Slayer Point Store for 100 slayer points if you want to top up.

Crystal chest

Opened with crystal keys. The reward table is bulk supplies and materials rather than uniques, including:

Uncut dragonstones, magic seeds and dragon bones
Dragon bolts and dragon darts
Rune platebody and platelegs
Super restores and manta rays
More crystal keys, so a stack partially refills itself

Useful for stocking up rather than chasing rares.

Beginner and tier chests from clues

Clue scrolls of every tier drop from a wide range of content, and clue geodes appear in the battle pass reward track. Clue rewards feed the collection log across all tiers.

If you are running clues regularly, the auto-salvage toggle is worth knowing about. From Adamant Supporter upward, ::cluesalvage automatically salvages rare clue rewards rather than making you handle them manually.

Getting more out of your keys

Open keys at higher supporter rank if you are close to a threshold. The save chance applies to every open from then on.
Use the higher slayer masters. Tier 3 and tier 4 keys are only available from Duradel, Krystilia and Nomad.
Drop rate bonuses apply. A drop rate scroll from your vote streak is worth using before opening a stack.