Samson Mow Highlights Criteria for Choosing a BTC L2 and Questions How to Exit Them

• The debate that sparked Mow's list: the ability to exit to the main chain despite a central operator.
• The creator of Spark responded and defended the operator model of his protocol.

Samson Mow, investor and CEO of JAN3, published on July 12 on X a list of eight criteria for choosing which second-layer (L2) Bitcoin network to build or operate on. The list arises amid what the investor considered a growing discussion about three protocols: Liquid Network, Ark, and Spark.

The eight criteria Mow lists, in order of priority, are as follows:

• Privacy: whether the operator can see or record the amounts and assets of each user.

• Operator model: whether a single entity or a federation can steal funds or censor someone.

• Liquidity: how easy it is to enter and exit the network with volume.

• Time in production: how long the network has been operating under real conditions.

• Data availability: whether the user can prove what they own without relying on the operator.

• Economically viable exit: whether the cost of exiting to the main chain is affordable or merely theoretical.

• Unilateral exit: the ability of a user to withdraw their funds back to the Bitcoin base layer (L1) independently.

• Activity requirements: whether the user needs to connect periodically to the network to avoid losing their funds.

Samson Mow Chose Liquid Network

Based on his criteria, Mow ranked Liquid Network, the chain created by Blockstream, first, Ark second, and dismissed Spark for being centralized. Mow and JAN3 build the Aqua wallet on Liquid, so his choice is also biased by their commercial relationship. Additionally, Mow has also worked for Blockstream and has a good relationship with Adam Back, co-founder of that company. Samson Mow presented 8 criteria for choosing a Bitcoin L2. Source: @SimplyBitcoin -- YouTube.

According to the data Mow provides about Liquid (a private network made up of companies), this chain operates with 15 functionaries, the entities that jointly sign transactions and validate movements between the main chain and this side network. They operate under a scheme of 11 out of 15 signatures and with hardware security modules (HSM).

Regarding liquidity, according to the CEO of JAN3, Liquid has a total value locked (TVL) of USD 5 billion, of which over USD 4 billion would correspond to tokenized assets and about USD 97 million to the stablecoin USDT, which would eliminate the problem of not being able to enter or exit with high-volume movements, an aspect that Mow highlighted.

Mow also states that Liquid offers confidential transactions by default, which hide the amount and type of asset of each operation even from the functionaries themselves, that the network has been in production for about seven and a half years since October 2018, and that its average fee is 0.1 sat/vB (satoshis per virtual byte, the unit used to measure the cost of a Bitcoin transaction).

Regarding unilateral withdrawals, Mow himself acknowledges that Liquid does not yet offer this to regular users. According to his post, the feature would arrive through a bridge using BitVM technology (a computational tool that allows for the verification of complex Bitcoin calculations without relying on a single party), which is planned in the network's roadmap, although no implementation date has been set. Meanwhile, those who join as members of the federation can perform a peg-out (a direct withdrawal from the sidechain to the main chain) without relying on third parties.

In his entire post, Mow does not mention the Lightning Network (LN), another instant payment network built on Bitcoin, which operates with payment channels between two parties (peer-to-peer) instead of a centralized operator or a federation, a model different from Liquid, Ark, and Spark, although technically more complex for its users.

The executive of JAN3 emphasized that a decisive factor in choosing an L2 has become the unilateral withdrawal: the ability for a user to withdraw their funds to the main Bitcoin chain on their own, without needing the cooperation of the operator, even if that operator acts maliciously, censors the user, fails, or disappears.

The three L2s mentioned by Mow allow for moving Bitcoin (BTC) outside the main chain, with faster and cheaper transactions, but in exchange for a variable degree of trust in the operator of that network. Depending on the design of each L2, that operator can be a single company, a federation of several, a server, or a set of participants validating the movements between that layer and the main Bitcoin chain.

The Cost of a Unilateral Withdrawal in Ark and Spark

The unilateral withdrawal contemplated by Bitcoin L2s like Liquid, Ark, or Spark implies that the user does not need to wait for the operator to confirm anything or give the green light to recover their funds, because they already have what they need to withdraw on their own to the main Bitcoin chain. This independence prevents funds from being trapped if the network operator fails, disconnects, or acts in bad faith.

However, the challenge for L2s is that this independent withdrawal mechanism often turns out to be slower, more expensive, or less practical than a cooperative withdrawal, that is, one in which the operator does participate and helps process the withdrawal. For this reason, many networks reserve unilateral withdrawal as a last resort, rather than offering it as the usual path.

In this regard, the investor and executive of JAN3 calculated how much it costs to exit Ark or Spark on one's own. He took as an example ten small balances, expressed in VTXO (virtual UTXOs), the unit with which these two networks register each user's funds before they become a common Bitcoin transaction.

Those ten balances considered by Mow total 100,000 satoshis. According to his calculation, withdrawing them from the network on one's own, with a fee of between 5 and 10 sat/vB, could result in a loss of between 40% and 100% of their value. That is, a good part of the money would go towards the transaction cost, according to Mow's estimate. The reason, as he explains, is the way Ark and Spark group the balances of many users within the same transaction on the main chain. Mow refers to that structure as tree, branch, and leaf. Withdrawing a small balance individually means dismantling that entire structure on the chain, not simply sending a transaction, which would increase costs.

Mow also states that, so far, only Spark effectively offers unilateral exit, while the rest promise it for later. This contrasts with an announcement from Lightspark, the company behind Spark, which in July 2025 reported that the feature was already available at the protocol level. This leaves open a distinction between what the protocol allows and what each wallet effectively exposes to its users in practice.

What Do the Documents from Ark and Spark Say? {#h-que-dicen-los-documentos-de-ark-y-spark}

The documentation from Second, the company developing Ark, explains that an emergency unilateral exit is possible at any time for funds newly entered into the network, without the Ark server being able to prevent it. The risk arises with already spent balances, where an exit could be exposed to double spending if the sender and the server act in collusion, something the user avoids if they refresh those balances before attempting the exit.

In Spark, as explained by Lightspark when announcing the feature, the mechanism works differently: upon depositing funds, the user receives in advance a pre-signed exit transaction, which can be transmitted to the main chain after a temporary lock (timelock), even if the operator is offline or attempts to censor it.

Finally, Kevin Hurley, creator of Spark, responded in a post on X this July 12 that the unilateral exit has existed in Spark since the early days of the network, that it does not require signature operators to be online, and that it requires a technique called CPFP (child pays for parent, the practice of paying a higher fee in a subsequent transaction to accelerate the confirmation of another one it depends on), designed so that it is not advantageous for an attacker to interfere.

Hurley explained that the network code of Spark, which imposes the rules of the protocol, is open source and added that the Spark service provider (SSP), an optional role within the network, does not hold users' seed phrases nor can it freeze funds.

Hurley concluded by pointing in the opposite direction towards Ark, which he blamed for relying on a single operator capable of taking a user's funds if they do not connect to the network for 28 days, without either party providing an independently audited comparison between both models.

In this context, Mow laid out his 8 criteria for choosing a Bitcoin L2, while the community discusses ways to exit unilaterally.

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