Navigating the Hard Fork

Sia 2.0 marks an important milestone in the network's history and its biggest update so far. Not only you will be using Sia through a new and more performant set of apps, each named after its purpose, but Sia is also migrating its blockchain to a new and more efficient format allowing instant syncing and opening doors for a lot of new applications.

This guide will explain everything in a language you can easily understand:

If you're a host, you should have this in your hostd.yml before July 4th (it's default, but only for the mainnet version) in order to enable RHP4.

You must also make sure your RHP4 port is open to the internet. If you use a non standard port you must make the addition to hostd.yml with your chosen port and make sure it is open to the internet.

rhp4:
  listenAddresses:
    - protocol: tcp # tcp, tcp4, or tcp6
      address: :9984

What is RHP4 and what is the location of hostd.yml?

RHP4 is the next generation of renter-host protocol for the Sia storage network. It dramatically increases performance compared to RHP3, improves contract payouts, reduces collateral lockup, and enables features necessary for light clients.

Operating System	Config File Location
Linux, FreeBSD, OpenBSD	`/etc/hostd/hostd.yml`
macOS	`~/Library/Application Support/hostd.yml`
Windows	`%APPDATA%\SiaFoundation\hostd.yml`
Docker	`/data/hostd.yml`

Anything else to know?

siad should be considered dead because renterd is ignoring siad hosts and there are most likely no siad renters left.

Hard Fork Phases

Pre-Hard Fork

Only v1 transactions are allowed.
There is only the v1 (legacy) Sia blockchain.
Supported Wallets:
- Sia-UI (28/29-word seed)
- Sia Central Lite Wallet (12 or 28/29-word seeds, Ledger)
- walletd (12-word seed, Ledger)

June 6th, 2025

Both v1 and v2 transactions are allowed.
Since the block height 526 000 (~6:00 am UTC), both the v2 and legacy blockchains are running in parallel.
Supported Wallets:
- walletd (12-word seed, Ledger)
- Sia Central Lite Wallet (12 or 28/29-word seeds, Ledger)
- Sia-UI (only withdrawals, see below)

July 4th, 2025

Only v2 transactions are allowed.
By the block 530 000 (~2:00 am UTC), migration to a new blockchain format is complete.
Supported Wallets:
- walletd (12-word seed, Ledger)
- Sia Central Lite Wallet (12 or 28/29-word seeds, Ledger)

Benefits & Consequences

This hardfork is introducing Utreexo (see details below), making Sia probably the world's first Utreexo-native blockchain. It comes with many benefits that are crucial for Sia to scale and to deliver a truly decentralized storage network without compromises.

What is Utreexo?

Today, blockchains are not just a full transaction history of the network but each block also contains a state, the data needed to validate new blocks. This is huge and evergrowing pile of data. And even if you dropped the whole history, the state required to validate a Sia block is very large, probably close to a few GB.
Blockchains also have an enormous databases of UTXOs (unspent transaction outputs) that Utreexo replaces with simple accumulator that provides same core functionality is a database: it lets you add new elements and it lets you ask if some element is present or not. It does even better as it doesn't let you remove an element, which fixes potential consensus issues of other blockchains.
Utreexo changes the way we design and implement blockchains by separating the transaction history from state which reduces its size down to few Kb.
This allows new users to skip the long syncing process by downloading one of these states from a peer (or an explorer) very quickly and fast forward to a particular "checkpoint" that is used to initialize the new Sia node.

Want to learn more?

Sia Blog: Utreexo in Sia: A Summary (2021)
Luke Champine: Utreexo in Sia: An Overview (2021)
Luke Champine: Utreexo in Context (2022, MIT Bitcoin Expo)
Luke Champine: Actually Functional Blockchain Design (2024, Lambda Conf)

Sia software went through radical overhaul over last few years, bringing huge performance, scaling and user experience upgrades. Sia-UI is now deprecated and instead there is a new set of modern looking apps, each with its own purpose: walletd for wallet users, renterd for renters, hostd for hosts and explorerd for exchanges or mining pools.

Main advantage of Utreexo is in how vastly easier it is to join the network as a full node. Previously you couldn't do anything until you finished syncing. That process took days and in same cases even more than a week as the main bottleneck was your HDD and if you didn't have SSD it took way too long. With 2.0, you can not only download the state of network in form of few Kb, but you can also download individual blocks in parallel, taking the full sync time down to under an hour. The main bottleneck in 2.0 is mostly your internet bandwidth which means that with a good connection this could even get down to minutes.

It also opens door for existence of many new features and tools like the lite node (see detail below), or indexer which will let people use a 3rd party to manage their contracts (no more details known at time of writing).

Getting Ready

During this transition Sia will move away from the old 28/29-word seed towards the new 12-word seed. While there will still be options for you to migrate from old seeds post-fork, it's recommended to do it before it.

See our Wallet Migration Guide for detailed instructions.

You can also check the official guide - Things to Know About Sia's Upcoming Fork.

What if I miss it?

No worries. It doesn't matter if you check your old seed now or 10 yers later, it's only logical that there will always be a way for user to access coins from their old seed.

See our Wallet Migration Guide for more details.