Dencun is the next planned network upgrade on Ethereum Mainnet
which will implement Proto-Danksharding with EIP-4844.
This introduces transactions that can shard "blobs" of data for scaling L2 chains.
Dencun is a combination of two upgrades: (1) Deneb, the name for Consensus Layer upgrade, and (2) Cancun, the name of the Execution Layer upgrade.
This upgrade will center around EIP-4844, but will also include a few other proposals.
EIP-4844: Shard Blob Transactions
introduces a new transaction format for “blob-carrying transactions”
which contain a large amount of data that cannot be accessed by EVM execution,
but whose commitment can be accessed. The format is intended to be
fully compatible with the format that will be used in full sharding.
EIP-1153: Transient storage opcodes
introduces transient storage opcodes, which manipulate state
that behaves identically to storage, except that transient storage is discarded
after every transaction. In other words, the values of transient storage are
never deserialized from storage or serialized to storage. Thus transient storage
is cheaper since it never requires disk access.
EIP-4788: Beacon block root in the EVM introduces
commits to the hash tree root of each beacon chain block in the corresponding execution payload header. Store each of these roots in a contract that lives in the execution state and add a new opcode that reads this contract.
EIP-6780: SELFDESTRUCT only in same transaction
changes the functionality of the SELFDESTRUCT opcode. The new functionality will be only to send all Ether in the account to the caller, except that the current behaviour is preserved when SELFDESTRUCT is called in the same transaction a contract was created.
EIP-7516: BLOBBASEFEE opcode
adds an opcode that returns the value of the blob base-fee of the current block it is executing in. It is the identical to EIP-3198 (BASEFEE opcode) except that it returns the blob base-fee as per EIP-4844.