Overledger explained: the OS behind Quant

What Overledger is (and what it is not)

Quant describes Overledger as "an API-based technology which is simple to incorporate into any existing system that works with APIs". That sentence does most of the work. Overledger is not a new chain competing with Ethereum or XRPL for transactions. It is middleware: a layer that sits between a company's existing software and whichever distributed ledgers that company wants to use, exposing all of them through one consistent REST interface.

The "operating system" label that Quant used from the original December 2017 announcement is a metaphor. An operating system hides hardware differences behind one set of system calls; Overledger hides ledger differences behind one set of API calls. A bank's developers write to Overledger once and the gateway handles the specifics of signing a Bitcoin transaction versus calling a Solidity contract on Ethereum versus submitting a payment on the XRP Ledger.

This matters for anyone trying to value the project or compare it with rivals. Public interoperability protocols such as Chainlink's CCIP, Cosmos IBC or LayerZero run on-chain and are secured by validator or node sets. Overledger runs as a hosted service operated by Quant Network Ltd, a private UK company. Both are "interoperability", but the trust model is completely different. We unpack the alternatives on the blockchain interoperability page and compare the two biggest rivals in Quant vs Chainlink and Quant vs XRP.

Version history: from testbed to Platform and Authorise

Overledger has gone through three distinct eras. The first was the research-and-whitepaper phase: the concept was announced on 7 December 2017, a whitepaper followed in January 2018 and the token sale closed in April 2018. The 2018 design described four internal layers: Transaction, Messaging, Filtering & Ordering, and Application. That architecture is still the clearest way to understand what the gateway does internally, even though the marketing language has since moved on.

The second era was the move to production. Overledger 1.0 arrived as a testbed in June 2020, release 1.5 went to live production in January 2021 and 2.0 shipped on 27 April 2021 as the full release. On 13 September 2021 Quant launched Overledger Network (release 2.1.0), the first version where third-party "gateways" could join and relay traffic, initially for Bitcoin, Ethereum and the XRP Ledger. Release 2.1.5 in December 2021 introduced the licence fee payable in QNT, which is the origin of the token's utility story. Later point releases added Polkadot mainnet (2.2.5), the Tokenise beta with QRC-20 tokens on Ethereum, Polygon and XDC (2.2.9, April 2023) and mandatory multi-factor authentication (2.2.25).

The third era is the SaaS product. Overledger Platform launched on 27 June 2023 as a hosted, low-code environment with "flows" for token issuance, bridging and smart-contract calls, explicitly described as the same stack used in the BIS and Bank of England Project Rosalind experiment. Overledger Authorise followed on 10 October 2023, adding what Quant calls central-bank-grade key management and transaction signing for institutions. Together these two products are what a bank buys today.

A full company chronology, including the ISO work that predates the product, is on the Quant history page.

How a transaction flows through Overledger

The easiest way to understand the gateway is to follow one payment from a bank's system to a public chain and back. The details below combine the API groups documented at docs.overledger.dev with the architecture Quant has described in its release notes; the exact internal sequencing is not public, so treat this as a faithful simplification rather than a wiring diagram.

The important consequence is that the customer's software contains no chain-specific code. Adding a new network is a configuration change on Quant's side, not a rewrite on the bank's side. The equally important consequence is that every transaction passes through infrastructure Quant operates, which is the root of the centralisation critique discussed below.

A standards-based approach: ISO TC 307 and ISO/TS 23516

Quant's founder, Gilbert Verdian, proposed the blockchain standards work that became ISO/TC 307 in 2015 and, according to his own presentations to WIPO and NEN, convenes its interoperability working group WG7. That committee published ISO/TS 23516:2026, "Blockchain and DLT — Interoperability framework", in March 2026. It is a 24-page Technical Specification (ISO page ID 82098, which is why some media call it "ISO 82098"), not a full International Standard, and ISO's own committee page does not name convenors, so the WG7 role rests on self-reported sources.

Why does this matter for the product? Overledger's pitch to banks is that it follows a framework-style approach to interoperability, in which a neutral layer defines how ledgers are described, addressed and transacted with, rather than a bespoke bridge per pair of chains. Quant's current GitHub organisation also hosts message definitions for the Secure Asset Transfer Protocol (SATP), an IETF-track effort for moving assets between ledgers via gateways. Whether Overledger is formally certified against ISO/TS 23516 is not stated anywhere we could verify, so the honest summary is "designed by people who wrote the standard", not "certified to the standard".

mDApps, QRC tokens and multi-ledger tokens

Quant's FAQ defines an mDApp as an application that is "cross-platform, multi-DLT, and no longer bound to any single blockchain". In practice that means an application whose logic can read state from one ledger and write to another through the same API, for instance checking a tokenised-deposit balance on a permissioned bank ledger and then settling a bond on a public chain.

The token side is handled by QRC, Quant's family of chain-agnostic smart contracts. There are three token types: Base (fungible), Flex (fungible with extra controls) and Vari (non-fungible). They are ERC-based, so they deploy on EVM chains without modification, and the Tokenise feature creates them through low-code flows. Quant announced on 3 February 2026 that a Japanese patent had been granted for its "multi-DLT token" approach. We have not seen the patent text, so we cannot say precisely which claims it covers.

This is where the project's pitch to banks and its value to QNT holders start to diverge. A bank can issue tokenised deposits through Tokenise and pay its platform fee in US dollars; the current FAQ says "you can pay your platform fee in USD, or you can subscribe with QNT". Nothing in the UK Finance or Clearing House announcements says participating banks must buy or hold QNT. The tokenomics page goes through what the licence mechanism does and does not guarantee.

Fusion: the "Layer 2.5" sitting on top of Overledger

For most of its life Overledger moved transactions between ledgers but executed nothing itself. Fusion, announced around 26 May 2025 and live on mainnet on 2 June 2026, changes that. Quant's own explainer describes a three-part stack: "Overledger connects (interoperability layer); QuantNet establishes trust (programmable settlement network); Fusion controls (multi-ledger rollup execution environment)".

Technically, Fusion is an optimistic rollup extended from the OP Stack; Quant maintains a fork of op-geth on GitHub. Execution data lives on a permissioned Hyperledger Besu network, and state roots are posted to multiple Layer 1s rather than a single one, which is what Quant means by "multi-ledger rollup". The marketing term "Layer 2.5" signals that it sits between a conventional Layer 2 (anchored to one chain) and the institutional networks that need privacy, KYC'd operators and jurisdiction controls.

Three design choices stand out for a finance reader. First, unified tokens (uTokens such as uUSDC or uBUIDL) represent an asset across chains without the classic lock-and-mint bridge contract that has been the target of the industry's largest hacks. Second, Trusted Nodes are KYC-verified operators that can select the jurisdictions they serve; these operators are meant to stake QNT, although the public parameters (minimums, lock-ups, yields) had not been published as of November 2026. Third, Quant Network Ltd acts as the sequencer, which keeps the company in control of ordering. The ecosystem page covers Fusion, QuantNet and Quant Flow as products; staking explains why "QNT staking" is still mostly a future tense.

Developer access, documentation and pricing

The developer hub is docs.overledger.dev. It groups the API into RPC, Deposits, Contracts, Stakes, Nodes, Networks, Flow Sessions, Flow Registry, Flow Query, Webhooks, Swaps, Withdrawals and Tracker, with guides for the Fusion Rollup, the Fusion Firewall and staking. Older hostnames that circulate in forum posts (docs.quant.network, developer.quant.network) did not resolve when we checked on 2 November 2026. The "Connectors" page describes self-serve onboarding for EVM, Solana, Cosmos, SUI, Hedera and Aptos networks, with permissioned or operator-gated ledgers such as XRPL, Stellar and Bitcoin available by request.

On GitHub, the quantnetwork organisation is verified and holds 15 public repositories, but most of the SDKs (overledger-sdk-javascript-v2, overledger-sdks, the demo app) are archived. The actively maintained repositories are the PayScript language specification used by Quant Flow, the op-geth fork behind Fusion, the SATP message definitions and the documentation site. Developers should therefore expect to work against the REST API directly rather than a first-party SDK.

Enterprise deployments: who actually uses it

Quant's reference list has grown markedly since 2023, and the useful filter is counterparty confirmation: deals announced by the bank, clearing house or vendor on the other side, not only by Quant. On that test, these are the deployments with primary-source evidence.

UK tokenised sterling deposits (GBTD)

UK Finance selected Quant on 26 September 2025 to build the platform for the Great British Tokenised Deposit pilot with Barclays, HSBC UK, Lloyds, NatWest, Nationwide and Santander; Monzo joined in January 2026. On 24 September 2026 UK Finance announced the first live customer transactions, including two remortgage completions where funds were locked and auto-released and an online-marketplace purchase. This is the clearest case of Overledger running real money for real customers.

The Clearing House (US)

Also on 24 September 2026, The Clearing House, operator of the RTP and CHIPS payment systems, said it had selected Quant to provide "the interoperability, orchestration, and transaction-management layer" for its bank-led On-Chain Money Initiative, with availability to participating institutions expected in the first half of 2027. QNT roughly doubled in price on the news and gave most of it back within days, a pattern worth remembering when reading announcement headlines.

Murex and earlier work

On 25 March 2026 Murex announced that Overledger and Quant Flow are embedded in MX.3, its capital-markets platform, for tokenised deposits and digital-bond settlement. Murex says ten clients use MX.3 for digital assets, but no bank using Quant through Murex is named. Earlier engagements include supplying infrastructure to the vendor team on the BIS and Bank of England Project Rosalind (completed June 2023), the UK Regulated Liability Network experimentation phase with R3 (2024), the SIA/Nexi interoperability test (2020) and LACChain in Latin America (2021). The CBDC page and partnerships page have the detail and the caveats.

Limitations and criticisms

A fair review has to weigh the gateway model honestly, because its strengths and weaknesses are the same design decision viewed from two sides.

The centralisation point deserves one more sentence. For a regulated bank, a single accountable vendor with a contract, SLAs and a KYC'd operator set is a feature, not a bug; that is why Quant wins tenders that permissionless protocols are not even invited to. For a crypto investor hoping the token captures protocol value, the same fact is a problem, because a gateway can be swapped out or priced in dollars. Both readings are correct. Our Quant review weighs them against each other, and the what is Quant page gives the plain-English overview if you arrived here first.