Monero's FCMP++ upgrade: the next hard fork explained
FCMP++ (Full-Chain Membership Proofs) is Monero's next big privacy upgrade. It replaces today's ring of 16 possible sources per input with a proof that a coin comes from the entire set of eligible outputs on the chain, and it ships with a new addressing scheme called Carrot. It is on a test network, and as of October 2026 there is no mainnet date.
The short answer
Today, each coin you spend on Monero hides among 15 decoys. FCMP++ would hide it among every eligible output on the blockchain, well over 100 million. The upgrade also changes how wallets derive keys and scan for payments (Carrot) and adds features needed for hardware wallets. It requires a hard fork, meaning every node and wallet must update.
As of 24 October 2026 the code is being tested on a public stressnet. No mainnet activation date has been announced. Any site giving you an exact date is guessing.
What changes
| Area | Today | With FCMP++ and Carrot |
|---|---|---|
| Hiding the sender | Ring signatures (CLSAG): real input plus 15 decoys | Membership proof over the full set of outputs |
| Decoy selection | Wallet picks decoys; poor choices can leak information | No decoys to pick |
| Hiding amounts | RingCT with Bulletproofs+ | Still hidden |
| Addresses | Standard addresses and subaddresses | Carrot, described by developers as backward compatible with existing addresses |
| Offline signing | Possible, but awkward | Hot-cold signing support added in testing, relevant to hardware wallets |
Why Monero wants it
The main known weaknesses of ring signatures come from the small ring. With 16 members, statistical analysis and "poisoned" outputs controlled by an observer can sometimes narrow down the real spend (see is Monero traceable?). FCMP++ removes that whole class of problem, because there is no small group to analyse.
FCMP++ is based on Generalized Bulletproofs. Its research proposal on the Community Crowdfunding System, posted by developer kayabaNerve on 13 April 2024, asked for 2,000 XMR to pay outside experts for proofs, formal verification and audits. A separate CCS proposal funded the firm CypherStack to review the Carrot specification in October 2024.
What is Carrot?
Carrot is the new addressing protocol and wallet key hierarchy that comes with FCMP++. It changes how wallets build and recognise outputs internally. Developers say existing addresses will keep working, so you should not need a new address to receive funds. Wallet apps will need significant updates to support it.
What happened to Seraphis and Jamtis?
For years the planned next step was Seraphis, a new transaction protocol, with the Jamtis address format. The developer working group's own documentation describes development priority switching from Seraphis to FCMP++ with Carrot. Seraphis is not scheduled.
Status and timeline (October 2026)
| Date | Milestone |
|---|---|
| 13 April 2024 | FCMP++ research and audit proposal posted on the CCS |
| 11 October 2024 | CCS proposal for CypherStack's Carrot specification review |
| 2026 (Q1) | Developer CCS reports describe Carrot and FCMP++ integration work and outreach to hardware wallet makers |
| 25 September 2026 | Stressnet release v0.19.0.0-beta.3.0 |
| 5 October 2026 | Stressnet v3.0 forked at block 3,102,800, adding hot-cold signing, Transaction Relay v2 improvements and RandomX v2 support (test network only) |
| Not announced | Mainnet hard fork |
Meanwhile the current mainnet software line continues: Monero 0.18.5.0 was released on 11 May 2026, followed by point releases 0.18.5.3 and 0.18.5.4 in October 2026. These are recommended updates, not hard forks.
What you need to do
- Nothing yet. Your coins are safe where they are. There is no token swap and no need to move funds.
- When a date is announced, update your wallet app and, if you run one, your node before the fork height. Wallets that are not updated will stop working on the new chain.
- Hardware wallet users: check that your device maker still maintains its Monero app. Ledger and Trezor will need firmware or app updates. See Monero hardware wallets.
- Keep your seed safe offline. Updated wallets restore from the same seed. See restore a Monero wallet.
- Ignore "upgrade" emails and pop-ups. Monero does not announce updates by email. In May 2025 a fake "Monero interface update" email led to a getmonero.org clone that installed remote-access malware. Get software only from the official downloads page, typed by hand. More in Monero scams.
Trade-offs and open questions
- Complexity. FCMP++ uses newer cryptography than ring signatures, which is why proofs and audits are part of the plan before activation.
- Performance. Verification and transaction size will be different from today. Final figures will only be known after testing ends.
- Wallet readiness. Every wallet, light-wallet server and hardware wallet app needs work. Smaller or unmaintained wallets may not make it.
- Timing. Monero has no company setting deadlines. Activation happens when developers consider the code ready and node operators adopt it, which can take months or longer.
For the background on earlier upgrades, see Monero history.
Frequently asked questions
When is the FCMP++ hard fork?
No mainnet date had been announced as of 24 October 2026. The upgrade was running on a test stressnet that forked to version 3.0 on 5 October 2026.
What does FCMP++ stand for?
Full-Chain Membership Proofs, with the plus signs referring to the extended design used for Monero. It proves a spent coin is one of all eligible outputs on the chain instead of one of 16.
Will I need a new Monero address after FCMP++?
Developers describe the new Carrot addressing scheme as backward compatible with existing addresses, so existing addresses are expected to keep working.
Do I need to move my XMR before the upgrade?
No. There is no token swap. You will need to update your wallet software when the fork is scheduled. Anyone asking you to send coins or enter your seed to upgrade is a scammer.
Will my Ledger or Trezor work after FCMP++?
Only if the maker updates its Monero support. Developers have been working with hardware wallet makers, and the test network added offline signing support, but check your vendor's announcements before the fork.