In crypto, MEV typically refers to bots and searchers on chains like Ethereum reordering, inserting, or censoring transactions around DEX trades and liquidations to extract value from users in the form of worse prices, failed transactions, and higher costs.
However, did you know that Bitcoin also has MEV-like dynamics at the mempool and policy layer? It’s akin to its own quiet version of MEV, without DeFi-style bots front-running swaps. Instead, miners and pools use fee signals, mempool policies, and block templates to determine which transactions clear first.
Yet, the public mempool is only part of the auction that determines which transactions are cleared in the next block, as out-of-band routes to pools and wallet-level fee controls also play a role.
Within the Bitcoin network, miners and pools are effectively the decision-makers. They ultimately decide which consensus-valid transactions are included in blocks, based on the mempool and policy settings they use.
Bottom line: Bitcoin has a soft form of MEV for everyday users. Small fee changes, package construction (parent + child), and direct-to-pool paths can nudge your transaction ahead of others, even when they were broadcast first.
When a miner assembles a block template, transactions are effectively selected in this rough order:
In practice, this is how miners quietly decide which transactions ‘win’ the next block.
Compared with Ethereum and DeFi MEV, where searchers run arbitrage, sandwich, and liquidation bots to extract value from smart‑contract interactions, Bitcoin’s “soft MEV” is quiet.
There is no front-running of DEX swaps or liquidation auctions; instead, miners and pools adjust their ordering via fee-based incentives, package selection, and occasional off-chain payments. That contrast is why this MEV is far less visible to the average user.
Hourly windows in October showed bursts and near-empty gaps on mempool.space’s block fee rate view, creating periods where a minor absolute fee delta can move a transaction to the top of a template.
With ancestor-feerate mining and package relay, the practical fee auction is increasingly package-based rather than naively per-transaction.
This is why child-pays-for-parent routinely pulls stuck parents into a block when the combined package clears the miner threshold.
The same release also introduced opportunistic 1-parent, 1-child package relay and made TRUC (version 3) transactions and P2A outputs the standard by default, along with a limited form of package RBF.
Later Core versions (v29+) maintain full-RBF as the default mempool policy and continue to evolve package relay.
These arrangements can skew template selection and reduce transparency when they occur frequently, as the on-chain feerate alone no longer explains inclusion.
Policy filters, which govern relay but not consensus validity, are a second lever that affects which transactions reach miners on time. Standardness policies are not consensus rules; miners can include any consensus-valid transaction even if relay nodes drop it.
The recent OP_RETURN change illustrates how defaults shape propagation. Developers merged a shift in the v30 cycle, removing the long-standing ~80-byte default limit for OP_RETURN in policy, raising the default data carrier size, and later tweaking how node operators can configure it.
Public episodes also illustrate discretionary filtering at the pool layer. OCEAN chose to filter inscription-style data, and Marathon’s 2021 OFAC-compliant experiment showed template selection can deviate from a pure max-fee ranking when pools pursue policy or public relations goals.
The rules governing replacements and packages establish the practical limits of priority. BIP125 requires a replacement to pay a higher absolute fee than all conflicts and also cover a minimal incremental relay fee.
Yet, RBF rules (including BIP125) are mempool policy, not consensus. Miners can always mine any consensus-valid replacement they see first.
Wallets that fee bump often aim to leap to the next block’s fee rate bucket with a material increase to avoid repeated churn, a heuristic rather than a rule. CPFP remains a direct way to source a fee when a parent is stuck, and a 1-parent, 1-child relay in v28 raises the probability that a fee-sponsoring child arrives in peer mempools quickly enough to change the following template.
From your perspective as a wallet user, tiny decisions in how you set fees or structure transactions can quietly move you up or down the miner’s queue.
Queue-jumping via RBF is commonplace: a higher-fee replacement can overtake earlier broadcasts. CPFP allows you to sponsor a stuck parent by paying from a child, thereby raising the package’s effective fee rate. Direct-to-pool accelerators act as an emergency lane when public mempools are congested.
In practice, small fee deltas and package construction are the “soft MEV” edges that decide who clears first.
Consider two similar transactions: Alice sends a payment with a modest fee while Bob uses RBF to bump his fee by a few sats/vB. Even if Alice broadcasts first, Bob’s higher replacement can leapfrog into the next block under BIP125.
Or imagine a stuck parent transaction rescued by a child; if you attach a child with a high fee, the combined package often wins inclusion sooner than a single high‑fee transaction with no dependencies.
Likewise, a transaction with a low on‑chain fee rate can still win if you use a pool accelerator to pay the fee out‑of‑band.
These ideas aim to make deviations from fee maximization easier to spot, whether due to OOB compensation, policy filters, or simple latency.
The forward path depends on fee levels and burst frequency, and the incentives scale as the block subsidy shrinks below 3.125 BTC over future halvings.
If average fees remain around $1–$2 and fee share holds near low single digits, most soft MEV activity will come from modest RBF bumps and CPFP around anchors, with OOB used as an emergency lane.
If bursts recur around inscriptions, headlines, or a looser OP_RETURN policy environment, average fees can jump into higher brackets for short windows. Fee share can reach the high single digits on spike days, and out-of-band paths and package bidding will become more apparent in template and block diffs.
The mechanics remain straightforward. Miners build templates using ancestor-aware scoring, wallets, and service source fees, with RBF and CPFP as specified in BIP125. Package relay was introduced in Core v28 onward, and OOB lanes provide pools with a direct channel for priority.
That’s the quiet MEV of Bitcoin: miners and pools don’t front‑run your swaps, but they do quietly pick winners in your mempool using fees, packages and side channels.
