ACINQ

ACINQ is a Paris-based Bitcoin technology company specialising in the development and operation of Lightning Network infrastructure, most notably the Eclair Lightning Network node implementation written in Scala and the Phoenix self-custodial mobile Bitcoin wallet. The company operates one of the largest publicly reachable Lightning Network routing nodes, providing significant liquidity and routing capacity to the network. ACINQ contributes to the BOLT (Basis of Lightning Technology) protocol specification process and has pioneered features such as trampoline routing to reduce the on-device computation required by mobile Lightning clients.

Overview

• ACINQ was founded in 2014 in Paris, France, originally focused on Bitcoin tooling. As the Lightning Network white paper emerged (Poon & Dryja, 2015) the company pivoted to become one of its three flagship node implementation teams, alongside Lightning Labs (LND) and Blockstream (Core Lightning).
• The company’s dual mission is (1) to provide a robust open-source Lightning Network implementation suitable for routing nodes and infrastructure operators, and (2) to make Lightning Network payments accessible to non-technical end-users through Phoenix, its consumer-facing wallet.
• ACINQ operates ACINQ.fr, a publicly advertised super-node with a large number of open channels, which acts as a hub to which Phoenix wallet users connect by default, enabling Trampoline Routing — a technique ACINQ invented and proposed as a BOLT extension to delegate path-finding computation from resource-constrained mobile devices to well-connected routing nodes.

Key Components

Eclair

• The flagship open-source Lightning node implementation, written in Scala Programming Language using the Akka actor framework.
• Targets server-side routing node operators and institutional Lightning infrastructure.
• Supports all core BOLT features: HTLC forwarding, Onion Routing (layered Sphinx Routing), Payment Channel lifecycle, and cooperative/force-close flows.
• Implements Trampoline Routing, Splicing, Anchor Outputs, and BOLT 12 offers.
• Exposes a JSON-RPC API and is used as the backend powering the Phoenix wallet’s server-side component.

Phoenix Wallet

• A Non-Custodial Wallet iOS and Android application connecting to ACINQ’s node as a trampoline hub.
• Users retain control of their private keys; channels are opened on demand using Splicing so a single channel can expand or contract without on-chain closure.
• Introduced the concept of a “zero-configuration” Lightning experience: inbound Channel Liquidity is provisioned automatically via a “dual-funded channel” or Splicing mechanism.
• Operates over Tor for enhanced privacy on supported platforms.

Trampoline Routing

• An ACINQ-pioneered protocol extension allowing a mobile Lightning Network node to delegate route calculation to one or more intermediate “trampoline” nodes.
• Reduces the requirement for clients to maintain a full Gossip Protocol routing table, critical for battery-constrained mobile devices.
• Preserves payment privacy through nested Onion Routing packets.

Splicing

• A protocol feature enabling the resizing of Payment Channel capacity — both increasing and decreasing — via a single on-chain transaction, while keeping the channel live for routing during the splice confirmation.
• ACINQ implemented splicing in Eclair and Phoenix before it was widely supported across implementations.

Applications and Use Cases

• Mobile Bitcoin Payments — Phoenix provides a user-friendly entry point to the Lightning Network without requiring users to manage channel balances manually, targeting everyday retail and remittance use cases.
• Institutional Routing Infrastructure — Eclair is deployed by exchanges, payment processors, and Bitcoin Layer 2 service providers that need a reliable, high-throughput Routing Node.
• Developer Tooling — The eclair-core library exposes Lightning primitives for integration into third-party applications, making ACINQ a building block in the broader Lightning developer ecosystem.
• Micropayment Streaming — The sub-satoshi precision of Lightning HTLC settlements enables value-streaming applications such as pay-per-second media or API metering; ACINQ’s infrastructure serves as a routing backbone for these flows.
• Cross-border Remittance — Phoenix’s fee-transparent model (swap-in/swap-out via Splicing) makes it suitable for low-value international transfers that are uneconomical on-chain.
• Proof-of-Concept for Protocol Innovation — ACINQ uses Phoenix as a live testbed for new BOLT features before they are standardised, meaning millions of Phoenix users act as a real-world deployment surface for emerging Lightning protocol capabilities.

Mechanisms

• HTLC (Hashed Time-Locked Contract) — The atomic swap primitive used to route payments through multi-hop Payment Channel paths; each hop holds funds conditionally pending a cryptographic pre-image reveal within a time window.
• Onion Routing / Sphinx Routing — Payments traverse the network inside layered encrypted packets; each routing node decrypts only the layer addressed to it, preserving sender and recipient privacy.
• Channel Liquidity Management — ACINQ’s node deploys automated liquidity management: closing depleted channels, rebalancing via circular payments, and using Splicing to top up without channel closure.
• Gossip Protocol — Lightning nodes broadcast channel announcements and updates; ACINQ’s node aggregates this Peer-to-Peer Network gossip to maintain a network-wide routing graph used by the Eclair path-finder.
• Anchor Outputs — A channel construction technique (adopted after SegWit) that allows fee-bumping of commitment transactions post-broadcast via Child-Pays-for-Parent (CPFP), improving safety under fee-market volatility.
• BOLT 12 Offers — A reusable, static payment descriptor format that replaces single-use Lightning invoices; ACINQ has been an early implementer and advocate.

Standards & Context

• ACINQ participates actively in the BOLT (Basis of Lightning Technology) specification process, which is the de-facto standards body for the Lightning Network protocol.
• Key BOLTs relevant to ACINQ’s work:
  • BOLT 1 — Base protocol message framing.
  • BOLT 2 — Payment Channel establishment and operation.
  • BOLT 4 — Sphinx Routing / Onion Routing packet format.
  • BOLT 7 — Gossip Protocol for peer and channel discovery.
  • BOLT 11 — Invoice encoding (the widely used lnbc... format).
  • BOLT 12 — Offers protocol (reusable static invoices), championed by ACINQ and others.
• The Bitcoin base layer provides settlement guarantees via Bitcoin Proof-of-Work Protocol consensus; ACINQ’s stack relies on SegWit transaction outputs (P2WSH / P2TR) for channel script constructs.
• As a French company (SAS legal form), ACINQ operates under EU financial regulation; self-custodial wallet design is partly motivated by regulatory positioning to avoid acting as a custodian.
• The Lightning Network as a whole operates without a central standards organisation; BOLTs are maintained collaboratively by ACINQ, Lightning Labs, Blockstream, and independent contributors via GitHub.

Provenance