Does FCMP++ affect block size or block verification times for miners?

Yes—FCMP++ can change both the space transactions take inside a block and the work needed to verify that block. For you as a miner, the important effects are transaction-proof size, verification speed, and how quickly new blocks reach you—not a direct change to RandomX mining speed.

Why transaction size can change

FCMP++ stands for Full-Chain Membership Proofs++. It is a proposed Monero upgrade that changes how a transaction proves it is spending a valid existing output without revealing which one. An output is a piece of Monero received in an earlier transaction.

Monero’s ring-based approach hides the real output among a small group of possible outputs. FCMP++ aims to expand that protection across the eligible chain history.

That changes the proof data carried by transactions. But “more possible outputs” does not mean every transaction must include the chain’s entire history. The proof represents that relationship compactly.

The useful comparison is the total transaction size, not one proof in isolation. FCMP++ changes or replaces existing transaction components, so simply adding its proof size to an old transaction would give you a misleading estimate. The final format and the number of inputs being spent both matter.

What that means for block size

A block packages transactions together. If transactions take more bytes, a block containing the same set of payments will generally be larger.

However, FCMP++ does not automatically make every block larger by a fixed percentage:

• Blocks with little transaction activity may remain small.
• Different transaction shapes can have different size changes.
• Monero’s block weight—the measure used for block-limit and reward-penalty rules—is not necessarily identical to its raw byte count.

Monero already has adaptive block-weight rules. FCMP++ should therefore be assessed alongside its final weight accounting, rather than described as a simple increase to a fixed block-size limit.

For your mining operation, larger blocks can mean more bandwidth, more stored blockchain data, and potentially slower transmission between nodes.

Why verification time can change

Before your node accepts a block, it checks its transactions and their cryptographic proofs. FCMP++ introduces different proof-checking work and supporting chain-state data, so verification performance can change too.

Crucially, verifying a full-chain membership proof does not mean scanning every historical output again for each transaction. Its design uses a compact mathematical representation of the output set.

Still, neither “full-chain” nor “compact” tells you the actual processing time. That depends on:

• The final implementation and optimizations.
• Your processor and available memory.
• How many transaction inputs the block contains.
• Whether the benchmark includes supporting state updates.

Treat precise speed claims cautiously unless they identify the code version, hardware, and workload tested.

What matters while you mine

FCMP++ is not itself a replacement for RandomX, Monero’s proof-of-work algorithm—the calculation miners repeat to compete for blocks.

Its mining impact is mainly around that calculation. Longer block validation or transmission can delay your switch to the newest chain tip, potentially increasing wasted work.

If you mine through a pool, including through a browser-based service, the pool’s node usually handles block validation. Any effect on you is mostly indirect; it is not automatically a reduction in your device’s mining speed.

The bottom line

FCMP++ can affect block space and validation costs, but you should not assume a fixed size increase or slowdown. Look for measurements of the final implementation on miner-relevant hardware, especially total block verification and transmission time.