Ethereum protocol support lead Tim Beiko of the Ethereum Foundation announced on December 20, 2021, that the network's first publicly accessible Merge testnet, named Kintsugi, was live and open for community testing. The launch marked the first time developers, validators, and infrastructure operators outside of core client teams could interact with an Ethereum network running on proof-of-stake (PoS) consensus rather than the existing proof-of-work (PoW) system, in which miners compete to validate transactions by expending computing power.

The testnet followed four short-lived internal developer networks and a major in-person interoperability event in Greece called Amphora, held October 2 to 9, 2021. Forty representatives from ten client teams (five execution-layer: Besu, Erigon, Geth, Nethermind, and EthereumJS; and five consensus-layer: Nimbus, Lighthouse, Lodestar, Teku, and Prysm) attended and successfully ran a 10,000-validator, 100-node test network through a live PoW-to-PoS transition. That milestone established the technical foundation on which Kintsugi was built. Sajida Zouarhi of Hyperledger Besu (Consensys) noted afterward that the focused in-person collaboration had saved her team "several months worth of work."

Post-Merge Ethereum runs two software layers simultaneously: a consensus layer (the Beacon Chain node, which manages validator agreements) and an execution layer (the legacy transaction-processing client). Each maintains separate network connections and API endpoints. Supported execution clients include Geth, Nethermind, and Besu. Consensus clients include Teku, Prysm, Lighthouse, Nimbus, and Lodestar. Beiko was direct about the implications for builders. "For application developers, as previously explained, not much will change," he wrote in the announcement. The EthStaker community was designated to support new testers through a dedicated Discord channel named #testingthemerge. Shortly after Kintsugi launched, in January 2022, the Ethereum Foundation retired the "Ethereum 2.0" branding, which had caused confusion among users about whether ETH1 and ETH2 were separate assets rather than layers of a single network.

Kintsugi was never intended as a permanent fixture. During testing, a core developer exposed client compatibility problems by manipulating block hash values, causing some clients to accept invalid blocks while others rejected them. The network ultimately lost its ability to finalize transactions. The Ethereum Foundation replaced Kintsugi with the Kiln testnet in March 2022. Kiln proved more stable and served as the template for subsequent testnet merges on Ropsten, Sepolia, and Goerli before the mainnet transition executed on September 15, 2022. According to ethereum.org figures, the Merge reduced Ethereum's annual electricity consumption by approximately 99.988 percent compared to PoW operation. EY Switzerland calculated that the carbon footprint per transaction dropped from 109.71 kg CO₂e under PoW to 0.01 kg CO₂e under PoS.

The name "Kintsugi" refers to a Japanese craft tradition of repairing broken pottery with gold, treating damage as a source of strength and as part of an object's history rather than a flaw to conceal. The Ethereum Foundation used it as a deliberate metaphor for the network transforming itself rather than being discarded and rebuilt from scratch.

The testnet's launch carried practical weight for developers in South Asia and Africa, two regions with among the highest rates of grassroots crypto adoption at the time. India ranked second and Pakistan third in Chainalysis's 2021 Global Crypto Adoption Index, which measured grassroots usage across transaction volume and peer-to-peer activity. Nigeria and Kenya placed in the top 20. For development teams across these markets, Kintsugi provided early access to the post-Merge two-layer architecture without waiting for mainnet. That lead time mattered for smaller studios that could not absorb extended migration timelines.

Ethereum's shift to PoS also introduced a structural constraint relevant to retail participants in lower-income markets. Running a solo validator node requires a minimum stake of 32 ETH, which exceeded $100,000 at 2022 prices. For individual participants in Nigeria, Kenya, India, or Pakistan, that threshold is out of reach without pooling services. Liquid staking protocols such as Lido allow users to contribute any amount and receive proportional rewards, though they introduce a layer of intermediary reliance that direct node operation does not require. The testnet phase made clear that broad retail participation in Ethereum's PoS system would depend on these intermediary services rather than direct node operation.

The energy reduction outcome also carried regulatory implications in markets where policymakers had cited crypto mining's electricity demands. India, in particular, had seen officials reference environmental costs when discussing crypto oversight. The Merge did not resolve India's broader regulatory uncertainty, but it reduced one frequently cited objection from the conversation.

Kintsugi is now fully deprecated. Its practical legacy is the testing process it initiated and the client bugs it surfaced before real funds were at stake. The Merge executed without incident on mainnet in September 2022, completing a transition that had been in development since the Beacon Chain launched on December 1, 2020.