Overview

Bitcoin Gold (BTG) is a hard fork of Bitcoin that took a snapshot after block 491,406 on 24 October 2017. The first post-fork block on the new chain is height 491,407. Anyone holding BTC (and controlling the private keys) at the snapshot received an equal amount of BTG.

The project’s primary goal was to reduce mining centralization by changing the proof-of-work algorithm from SHA-256 (dominated by ASICs) to Equihash, which was designed to be more accessible to GPU miners. The team hoped this would make mining more decentralized and open to ordinary users with consumer graphics cards.

Public mining of the new chain began later (around 12 November 2017) after a short post-fork “endowment” period.

Key Features at Launch

• ASIC-resistant PoW — Original Equihash (later changed).
• SegWit support — Inherited and retained from Bitcoin.
• Full two-way replay protection — SIGHASH_FORKID with ForkID = 79.
• Unique address format — Addresses begin with G or A to reduce accidental cross-chain sends.
• Per-block difficulty adjustment — More responsive than Bitcoin’s two-week retarget.
• 1:1 claim — Same private keys that controlled BTC at the snapshot controlled the corresponding BTG.

The Endowment (Post-Mine)

After the snapshot, the project mined approximately 100,000 BTG over 8,000 blocks (heights 491,407–499,406) at minimal difficulty. This has often been called a “premine,” although technically it occurred after the fork.

• ~5% was allocated as an initial reward to the core team.
• The remaining ~95% was placed into multi-signature wallets intended as an endowment for ecosystem development.
• A large portion of the endowment was time-locked (released gradually over years).

The endowment was controversial at the time and remains one of the most discussed aspects of the project’s launch economics.

Technical Specifications

2018 PoW Hard Fork

In July 2018 (around block height 536,200) Bitcoin Gold activated a further hard fork that changed the Equihash parameters to a new variant called Equihash-BTG (144,5) and switched the difficulty algorithm to Zawy’s LWMA. The change was partly a response to the emergence of Equihash ASICs and to earlier network security issues.

Security History

Bitcoin Gold suffered notable 51% attacks in 2018 and again in 2020. These attacks allowed double-spending and damaged confidence in the network. The relatively low hashrate of an Equihash (and later Equihash-BTG) chain made it a recurring target compared with SHA-256 chains that can draw on Bitcoin’s much larger mining ecosystem.

Historical Context

Bitcoin Gold was one of the earliest and most prominent forks of the 2017 wave. While Bitcoin Cash focused on larger blocks, Bitcoin Gold focused on changing who could profitably mine. It attracted significant attention and exchange listings at launch, but like most of the era’s forks it later declined sharply in hashrate, development activity, and market relevance.