Grin v5.0.0 network upgrade (Hard Fork 4: January 2021)

This post will be updated as there is progress, with an announcement in the comments section each time there’s a significant change.

Version 0.3
Dec 11 2020

Important Block Heights and Dates

Event Date or Block
Testnet Hard Fork Block Height 642_240
Testnet Hard Fork Date (expected) 2020-12-08
Hard Fork Block Height 1,048,320
Hard Fork Date (expected) 2021-01-15 (est.)


As previously announced, Grin is making network wide upgrades through four scheduled hard forks in the first two years after launch. These are set in the code to occur in rough intervals of 6 months, at every 60*24*7*26 = 262,080 blocks:

  • Hard Fork 1: 262,080 Completed successfully
  • Hard Fork 2: 524,160 Completed successfully
  • Hard Fork 3: 786,240 Completed successfully
  • Hard Fork 4: 1,048,320.

The fourth network upgrade is expected to happen in mid-January 2021. Compatible versions of grin node and grin-wallet will be versioned 5.0.0 or greater. grin-miner will be unaffected. The first releases of these are scheduled for December.

This post describes breaking changes, timeline and communications that will take place, with the intention that the upgrade goes as smoothly as possible and that ecosystem participants can make the necessary preparations. It will be updated as necessary with additional information once available, so ensure to come back to it regularly.

Important Information:

  • Grin v5.0.0 is a network wide upgrade. Apart from updating their binaries in order to use Grin after the upgrade, users are not required to do anything. Stored grins will not be affected. Beware of scams telling you to move your coins elsewhere.
  • Unlike the previous three network upgrades, there will be no new secondary PoW algorithm announced, or new solver provided. The network is now converging to mine the primary Cuckatoo PoW algorithm indefinitely.
  • Staying true to the initial commitment before launch, there are no further hard forks or network upgrades scheduled. Any future network-wide upgrades will be done ad-hoc through co-ordination in the Grin community.


The following is a list of targeted changes. This section will be updated as required.


  • Improve transaction fee calculation, as outlined in this RFC proposal, still open for comments and improvement suggestions.
  • Improve difficulty adjustment algorithm, as outlined in this RFC proposal, still open for comments and improvement suggestions.
  • (Partial) Parallel IBD: Preparation for support of an improved process for initial sync and download of blockchain data.


  • Late locking of outputs: Removing the need for outputs to be locked during transaction building before the final stage.
  • Remove http listener for external addresses: As per the deprecation announcement with v4.0.0, remove support for unsecured http listeners in favour of the slatepack standard.

Detailed contents & Status


Date Milestone Description
2020-10-13 Scope freeze New functionality, improvements, and fixes targeted for the upgrade are defined, and prioritised.
2020-11-24 Beta Binaries Release Release of grin, grin-wallet, grin-miner beta binaries.
2020-12-08 Testnet upgrade Launch of testnet hard fork and public testing.
2020-12-15 Release candidate binaries Release of grin and grin-wallet RC binaries.
2021-01-05 Final release Release of grin and grin-wallet binaries.
2021-01-17 (est) Mainnet upgrade Grin is forking to v5.0.0.

NB: Actual dates (but not the hard fork block height) may vary slightly based on the current circumstances.


Prior to the hard fork, the Grin community will communicate with the following medium:

Date Milestone Description
2020-10-30 Communication to exchanges and mining pools Communicate with exchanges and mining pools to make sure everyone is aware and are getting ready for the upgrade, offering assistance as required.
2020-12-01 1st Banner First banner on the website with a link to a summary of what will happen.
2021-01-03 2nd Banner Update banner on the website with binaries and urge ecosystem to upgrade.
2021-01-08 Final banner Update banner to urge mining pool and exchanges to upgrade.
Immediately following upgrade v5.0.0 banner Add a banner on the website informing about the hard fork, the changes introduced, and links to the latest binaries.


For any feedback, questions, concerns, or problems, please contact Daniel Lehnberg:


  • v0.1, Oct 14: Initial draft
  • v0.2, Nov 03: Correct date typo
  • v0.3, Dec 11: Added testnet fork height

The year of the β€œmainnet upgrade” table element is wrong, should be 2021.

Thanks, this is now fixed :+1:

You can fill in the testnet fork height now: 642_240


So there is no Grin33 algorithm and the Grin32 will be the final one, is it right?

From HF4, the PoW is Cuckatoo32+, which is a miner’s choice of
Cuckatoo32 or Cuckatoo33 or Cuckatoo34 or … or Cuckatoo63.
In practice, I expect we won’t be seeing any Cuckatoo33 (let alone others) for a long time, considering it has double the memory requirements, as well as the awkward word size.

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Thanks for your update. So could it be considered that no new algorithms will appear in the next 1 or 2 years? I want to buy an iPollo G1, but not sure how long it can work. According to my friend’s information, he said the algorithm should be changed this time, and Cuckatoo32 will be deprecated in August. Is it true?

No more change.
Your friend is misinformed.


Banner shows still 4.1.1.Not updated?

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The hard fork didn’t happen yet.

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as of now 7533 blocks remaining until hard fork.
Checkout our countdown clock at website.



We are ready for fork?


For such a break hard fork, can someone list here Exchanges which support the Slatepack/tor address transactions?

See here.

Thanks and that is a really nice list.

WHat does this mean for hodlers who have not accessed their cold storage in a while and thu sdo not have a TOR address?

Every wallet has a TOR address. Some have yet to show it though.

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I last interacted with my GRIN wallet in 2019 and never used TOR actively yet. Does that mean there is no action needed on my part?

Tor is just a new method to transact, it doesn’t have any other effect on your wallet. Your funds are safe.

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