Second, a Bitcoin development lab, has officially launched Bark — its implementation of the Ark protocol — on the Bitcoin mainnet, opening up self-custodial bitcoin payments to developers and everyday users alike without the complexity traditionally associated with Lightning Network or on-chain transactions.

Bark is built on the Ark protocol, a layer-2 solution that allows large numbers of users to share on-chain UTXOs via trees of pre-signed, off-chain transactions, spreading fee costs across participants while preserving individual self-custody. 

Unlike Lightning, Ark requires no channel management or liquidity pre-allocation, addressing pain points that have long kept mainstream users tethered to custodial alternatives.

“We wanted to make it ridiculously easy for users to get started with self-custodial bitcoin, hold it, and spend it, without surprise fees, and without having to manage channels or liquidity,” wrote CEO Steven Roose in a blog post.

As of today, Second’s Ark server is publicly accessible for payments. The launch includes a full developer toolkit — the Bark SDK — written in Rust with language bindings for Kotlin, Swift, React Native, Flutter, Go, Python, and WebAssembly. For server environments, Second also ships Barkd, a standalone wallet daemon exposing a REST interface with an OpenAPI spec.

Several applications are already mainnet-enabled at launch. 

Noah is a full-stack mobile Ark wallet pairing a React Native frontend with a Rust backend. Arke is a design-led native iOS wallet built around open-source UX principles from bitcoin.design. Satsigner brings Sparrow-style UTXO management and multisig workflows to mobile users.  Bark Wallet is an Umbrel app supporting Ark, Lightning, and on-chain payments.

A BTCPay Server plugin — also built by Second — lets merchants process self-custodial Lightning payments without opening channels or managing liquidity.

Second has raised $5.1 million from a private investor and operates with a team of 11. The company has drawn notable industry talent, including former Blockstream engineers.

The launch comes at a moment of heightened competition in the Bitcoin layer-2 space, with multiple protocols — including Ark Labs’ Arkade and statechain-based solutions — vying to close the gap between self-custody and user experience.

Second will also host a live AMA on Stacker News on June 9 at 10:00 AM EST.