OP_SECURETHEBAG is a new proposed opcode that uses a simple covenant to enable a set of valuable use cases like congestion controlled transactions, wallet vaults, CoinJoin and channel factories.

A new BIP being discussed on the Bitcoin-dev mailing list is aiming at making variable Bitcoin block size depending on the fee the sender is willing to pay, the BIP is aiming at making the block space small, decrease the impact of spam transactions, balancing fees with smaller fees increasing in a higher percentage than higher fees, allow larger block size if the sender is willing to pay for it, allow wallets to display the amount, and price, of free block space left and allow senders to have more control on their fee/priority structure.

Samourai Wallet is introducing Collaborative Transactions (Coohoots). This features two types of transactions based on the idea of collaborating with other parties and inspired from Greg Maxwell’s idea of nested/embedded transactions.

One of the main features intended for Bitcoin in the future is a native support for multisig payments and coinjoins, they are currently supported by the Blockchain but not in a native way and as such they do not have as much efficiency and privacy as desired. This is going to be the main focus of the next major update in Bitcoin, changing the signature scheme to Schnorr Signatures.

As a simplified alternative to Pay-to-Endpoint (P2EP - Pay-to-Endpoint), developer Ryan Havar proposed a BIP for a new coinjoins protocol that does not need changes to the current Bitcoin consensus and provides a simple, practical way to make coinjoin transactions that are indistinguishable from normal ones.

This is summary for a submission by Ruben Somsen on bitcoin-dev on censorship resistant transactions.

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Bitcoin transactions with light client wallets involve addition of transaction fees as incentive for miners to include the transaction to the blockchain through the process of mining. This creates a win-win situation.

First, without any specific conditions, miners get paid the fees provided the transaction gets included in a valid chain with the most proof-of-work.

Secondly, the user enjoys the benefit of his transaction being added to the blockchain. The fees also ensure the security of transaction on the network as miners cannot ignore the transactions or other miners will process it because it has a reward attached.

For the full node Bitcoin Core however, conditions for adding transactions to the blockchain are more specific, one of which is that transactions can only be added to a block with a block height that is one higher than the last.