Unbreaking testnet4

Mining approximately thirteen mainnet blocks at the current difficulty level would necessitate a substantial amount of hashing power, equivalent to forfeiting around $4 million USD in mainnet block rewards. This scenario underlines a commitment to permissionless mining, where the timing of chain reorganizations is of secondary concern. The potential interoperability between testnet5 and testnet4 blocks, allowing for a one-way acceptance of testnet5 blocks by testnet4 nodes, introduces a strategy for network evolution. Such an approach suggests a coordinated effort could enable a newer, initially weaker network to gradually outpace and replace its predecessor without necessitating a complete overhaul from the outset. This process hints at a more efficient transition, potentially reducing the time needed to supplant an existing chain significantly below thirteen years.

The different expectations of block difficulty between old and new clients highlight inherent compatibility issues, suggesting that adjustments are necessary for seamless operation across versions. The proposal treats CPU-mined blocks as inherently weaker, subject to reorganization, and introduces the concept of requiring blocks to meet a higher threshold than currently mandated by the "nBits" in the block header—a change characterized as a soft fork. This approach also allows for the potential inclusion of non-standard transactions from CPU-mined blocks in certain scenarios, provided the overarching requirement for real difficulty is maintained, thereby ensuring network integrity.

The discussion further explores the dynamic between ASIC and CPU mining, suggesting a framework where only ASIC-confirmed transactions are considered definitively confirmed. This system implicitly acknowledges the superior processing power of ASICs, capable of invalidating numerous CPU-mined blocks with a single ASIC-mined block. The resistance to such changes stems not from a lack of capability but from the absence of implementation in official versions and a general lack of awareness or technical proficiency among miners.

Finally, the discourse touches upon the strategic advantage of forcing legacy client upgrades through the distribution of new chains to old nodes, emphasizing the appeal of soft forks due to their non-disruptive nature. This method of upgrade promotes a smoother transition for the network by leveraging backward compatibility, making it easier to encourage updates among users of outdated software.