Bitcoin Classic is one of several forks of the Bitcoin reference implementation Bitcoin Core aiming to increase the transaction processing capacity of Bitcoin by increasing the block size limit. Blocks, which contain transaction data, form the basic structure of the immutable blockchain. Bitcoin Classic started out as similar to, though less aggressive than, the Bitcoin XT fork, which never managed to get the support it needed. Bitcoin Classic in its first 8 months promoted a single increase of the maximum block size from one megabyte to two megabytes. In November 2016 this changed and the project moved to a solution that moved the limit out of the software rules into the hands of the miners and nodes.
Bitcoin Classic is also an attempt to move the technical governance of this decentralized and independent Bitcoin project from the developers of the original Bitcoin to a voting process involving a larger community of miners, businesses, developers and users. There is no formal activation method for the software, but due to the nature of Bitcoin a supermajority needs to support it.
It claims support from developers: Gavin Andresen, Jeff Garzik, Pedro Pinheiro, Tom Zander, Jon Rumion, Peter Rizun and Sergio Lerner.
In Bitcoin, transactions are collected into blocks, and each block is produced by the bitcoin network on average every ten minutes. With Bitcoin's current limit of one megabyte, this capacity translates to an estimated average of three transactions per second. With Bitcoin Classic's proposed doubling of the block size limit to two megabytes, the maximum transaction rate would also roughly double. If deployed, Bitcoin Classic would render current Bitcoin software obsolete, as it changes protocol parameters, namely increasing the maximum block size from one megabyte to two megabytes. Most implementations of Bitcoin software would require small modifications to the block size limit in order to continue to work.
Bitcoin Classic has received support from some Bitcoin companies, developers, investors and miners, such as Coinbase, Bitstamp, Circle, Jeff Garzik, Roger Ver and Gavin Andresen. The Wall Street Journal said "Bitcoin Classic has emerged from the ashes of the XT versus Core debate. It is a version of Bitcoin that would allow for a two-megabyte limit. It appears to be quickly winning support."  However a hard fork was not seen as an urgent issue by the wider bitcoin community. Opponents argued that increased size of blocks will lead to increased system resource requirements for operating a full node, which in turn will lead to increased centralization. The software's peak use was observed in early 2016 with a steady decline in usage from March 2016 onwards.
On November 10, 2017, in the wake of the failure of plans for the hard fork to double the bitcoin block size, Bitcoin Classic ceased operation, declaring that Bitcoin Cash is now the only hope for bitcoin to become scalable.