What Are Conditional Transactions, and What Do They Change for DEX Swaps?

A conditional transaction is a signed order that the network holds until the blockchain's state matches conditions set by the sender. If they are not met within the given window, the transaction never enters a block. For a DEX swap this is a way to say "execute only if the pool is in the right state" at the network level, rather than inside a smart contract where a failed attempt still costs gas.

How does a DEX swap work without conditional transactions?#

The user signs a swap and sets a slippage tolerance — the minimum number of tokens they will accept. The transaction is included at the first opportunity. If the pool price has moved beyond the tolerance in the meantime, the contract reverts. The tokens stay with the user, but the gas fee is charged: the network did the computation before refusing. See our pieces on why a failed transaction still costs gas and how slippage and price impact work.

To execute a trade "at price X or better, sometime later," an intermediary is needed today: a limit-order contract, a bot or a network of solvers that watch the price and submit the transaction at the right moment.

What exactly shipped in Base's Cobalt upgrade?#

The layer 2 network Base activated its Cobalt upgrade on September 30, 2026 at 18:00 UTC. As TokenPost describes it, it includes so-called validity transactions: a signed transaction becomes eligible for inclusion only after conditions of four kinds are met —

• on an address balance;
• on a contract storage value;
• on a block number;
• on a Flashblock index — a sub-block inside the main block.

Three common Ethereum transaction formats are supported: legacy, EIP-2930 and EIP-1559. Parameter gives an example: a participant submits a swap that triggers only if an asset reaches a price threshold within a set time window. The network evaluates conditions as each block is built; if they are never met, the transaction does not execute. According to Base, such submissions can stay private until inclusion.

How is this different from a limit order?#

A limit order on an order-book exchange guarantees the execution price: the trade fills at the stated price or better. A conditional transaction guarantees something else — that it will not begin executing while the condition is false.

The condition is checked against chain state before execution. Between that check and the swap itself, other operations may land in the same block, and the pool price can change by the time the swap runs. So a slippage tolerance inside the swap is still needed: the condition filters out clearly unsuitable moments, and the tolerance protects at the moment of execution.

The conditions themselves also differ. A "contract storage value" is a specific data slot of the pool, not a human-readable price. Translating "price not below 2,500" into a condition on a slot is the job of the wallet or interface, and a mistake in that translation is a new source of risk.

What does this change for a DEX user?#

• Fewer paid reverts: an order whose condition is not met does not enter a block.
• Some scenarios that used to require a bot or a third-party solver can be expressed as one signed transaction with a validity window.
• An order that stays hidden until inclusion is harder for others to front-run.

What are the limits and risks?#

• TokenPost notes that at publication time, mainnet availability of conditional transactions had not been confirmed separately from the upgrade itself; wallet and DEX interface support will take time.
• The sources do not say whether any fee is charged for an order whose condition is never met.
• Conditions are checked by the block builder. On a network where one operator builds blocks, the user relies on that operator's honesty and uptime.
• Tokens with transfer restrictions remain subject to their own rules: per crypto.news, a conditional transaction is still checked against the token's policy at execution.
• The move to 200-millisecond blocks is not part of Cobalt and is deferred to the next upgrade; fee payment in B20 tokens was removed from scope on September 29.
• This is a feature of one network. On other networks the same scenario still needs contracts and solvers, and carrying habits across networks invites mistakes.