BIP 42, described in BIP-42, formally documented what was already a shared understanding: Bitcoin’s supply would never exceed 21 million BTC. The impetus was a floating-point overflow bug that could hypothetically lead to more minted coins.

By clarifying and ensuring the code respects that cap under all circumstances, BIP 42 reinforced Bitcoin’s hard limit. It’s a cornerstone of Bitcoin’s value proposition as ‘digital gold,’ where scarcity is algorithmically guaranteed. This BIP is both a technical patch and a symbolic declaration of the project’s commitment to a fixed supply.