Skip to main content
This page specifies the Sei Giga protocol as defined in the Giga whitepaper v2.0 (Marsh, Landers, Jog, Ranchal-Pedrosa; June 2026), with implementation notes from the sei-chain codebase as of the v6.6 release line (July 2026). The specification is forward-looking and subject to change until the corresponding upgrades activate on the Sei network. For a conceptual introduction, start with the Sei Giga overview; for practical guidance, see the developer guide.

​
Protocol at a glance

​
Network and security model

Giga’s fault model assumes n = 3f + 1 validator replicas, of which at most f are Byzantine, communicating over authenticated point-to-point channels with unforgeable cryptographic primitives. The protocol targets the partial synchrony model: safety is unconditional, and liveness requires only that the network eventually stabilizes so message delays respect known upper bounds.
  • Safety: no two conflicting proposals can both obtain a valid commit certificate in the same consensus slot. Attesting to two different divergence digests for the same finalized block will be slashable equivocation, because quorum intersection guarantees at least one honest validator would have to sign both.
  • Censorship resistance: once a proposal holds f + 1 availability votes, at least one honest replica stores its data, and a correct leader must include it in a future cut. Faulty proposers will not be able to disseminate data without it eventually being ordered, which bounds censorship to a finite delay. Users will also be able to submit a transaction to multiple validators at once (deduplicated at merge, with a partial tip refund).
  • Execution divergence: if fewer than 1/3 of validators compute a divergent state (hardware fault, software bug), the chain will continue while the fault is localized. Divergence beyond the Byzantine threshold will pause the chain, as in any BFT system.
  • Staking: validators will continue to bond SEI and can be slashed for malicious behavior. The complete slashing schedule, reward functions, and tokenomics for Giga are deferred to future work; today’s staking parameters are documented in Staking.

​
Consensus: Autobahn

Sei Giga will order transactions with Autobahn (Giridharan, Suri-Payer, Abraham, Alvisi, Crooks; 2024), a BFT protocol that decouples data dissemination from ordering. It occupies a deliberate middle ground between view-based protocols (HotStuff, Tendermint), which stall during network “blips,” and DAG-based protocols (Narwhal-style), which pay extra latency in the good case. Autobahn pairs an asynchronous data layer with a partially synchronous, low-latency ordering layer; it recovers cleanly after periods of asynchrony and matches DAG-class throughput at roughly half the latency.

​
Data dissemination: lanes and Proofs of Availability

  • Every validator r will maintain its own lane: an append-only, hash-chained sequence of transaction batches (called cars). A proposal is the tuple Prop = ⟨pos, batch, parentRef⟩ signed by r, where pos is the lane sequence number and parentRef is the hash of the previous proposal in the same lane.
  • Validators that receive a proposal will verify it extends the lane correctly and return a signed vote over its digest. Once the proposer collects f + 1 matching votes, it will assemble a Proof of Availability (PoA), a certificate that the data is retrievable.
  • f + 1 is sufficient because any such quorum contains at least one correct replica that held the full data when it voted, and that replica serves it until all correct replicas have it. Giga’s design deliberately keeps the smaller quorum (rather than 2f + 1) because commitment itself triggers full replication along the execution path; a larger quorum would only add certification latency.
  • The latest proposal in a lane holding a PoA is the lane’s tip. Lanes are hash-chained, so certifying a tip implicitly attests the availability of every earlier proposal in that lane, and consensus never re-certifies history.
All validators will disseminate batches in parallel, continuously, without waiting for consensus. Dissemination will therefore not be the bottleneck, and total bandwidth will scale with the validator count rather than one leader’s uplink.

​
Ordering: cuts of tips

Consensus will periodically fix a global order by committing a cut, a vector of every lane’s current certified tip:
  1. Prepare. The slot’s leader (chosen by stake-weighted selection, as in Tendermint) will bundle the latest certified tips into a cut proposal; replicas will validate the PoAs and broadcast prepare votes, forming a PrepareQC at n - f votes.
  2. Commit. Replicas will exchange commit votes over the PrepareQC; a CommitQC finalizes the cut. If the leader gathers only the minimum n - f commit votes, it will run an additional confirm phase, collecting 2f + 1 confirmations before the commit certificate is final.
  3. Pipelining. Slots will overlap: as soon as replicas see the Prepare message for slot s, they can begin slot s + 1, and the next leader may start proposing while the previous cut is still in its commit phase. With quadratic communication and pipelining, the effective cost will be a 1.5 round-trip slow path, versus 2.5 without pipelining and 3 full rounds in Tendermint.
Committing one cut will finalize every uncommitted proposal in every lane up to the referenced tips. A single consensus decision can therefore commit many blocks’ worth of data at once, which is why the whitepaper reports roughly 70 times higher block production than the single-proposer design (180 versus 2.5 blocks per second). Validators will vote on compact certificates only; a replica that is missing batch data will fetch it after commit, off the critical path.

​
Leader failure and recovery

If a leader fails to make progress, replicas will fall back to a standard view change: a timeout certificate will elect a new leader, and the protocol will resume. Data dissemination will continue in every lane throughout, so a view change will cost some ordering latency but no throughput. The Autobahn paper calls this “seamless” recovery from blips; chained-HotStuff-style protocols instead pay a hangover after asynchrony. Two consensus upgrades beyond launch are already specified:
  • Ambulance (arXiv 2606.25099) replaces the timeout race with a “protocol-rigged race”: non-leader replicas do useful persistence work on candidate cuts built from the same certified tips in parallel, so when a leader is merely slow (I/O contention, garbage collection, routing trouble) the slot can finish from existing recovery state instead of paying a full timeout. Planned as a core part of a future upgrade.
  • Hermes, a next-generation consensus protocol on the official roadmap; its whitepaper has not been published yet.

​
Execution

​
Two finality notions

Giga will separate what consensus decides from what execution produces: Unless stated otherwise, latency claims in Giga materials refer to ordering finality. Ordering finality is already irreversible (the transaction sequence can never change); state attestation finality adds a BFT-signed confirmation of the results of execution.

​
Deterministic block transition

For each finalized block, every executor will compute the canonical transition Apply(S_prev, context, block) → (S_new, receipts, gas, writeLog). Given the same pre-state, block context, ordered transactions, identical execution semantics, and serializable parallel execution, this transition is unique, so all honest executors will derive byte-identical results without communicating. A transaction that reverts will stay reverted; it will not invalidate the rest of the block. This determinism is what makes it safe to run execution entirely off the consensus critical path. The execution client is deliberately narrow: it processes transactions and nothing else, with no tracing or log search on the hot path. Incoming blocks are pre-processed in parallel (parsing, sender recovery, signature verification), while exactly one block executes at a time. Receipt generation and indexing happen after execution, so block n + 1 can start while block n post-processes.

​
Parallel execution: Block-STM-style OCC

Within a block, transactions execute concurrently under optimistic concurrency control (the Block-STM approach):
  • A later transaction t_j depends on an earlier t_i when t_i’s write set overlaps t_j’s read or write set. The block’s total order keeps this dependency relation acyclic.
  • All transactions start executing in parallel, each buffering its writes privately. A validation phase checks, for each transaction, whether any earlier-ordered transaction committed a write into its read or write set after it began; conflicting transactions are rolled back and re-executed.
  • The committed result is provably identical to sequential execution in block order (a “valid parallel schedule”). When contention is low, most transactions commit on their first attempt; under sustained contention the engine may fall back to sequential execution with unchanged semantics. In sei-chain, the scheduler retries a transaction up to 10 times before reverting to the sequential path.
Sei Labs measured that 64.85% of historical Ethereum transactions can be parallelized under this model. Contract-design guidance for maximizing parallelism is in the developer guide.

​
Transaction encoding

Giga will replace nested RLP with a flat, length-prefixed encoding designed for single-pass, zero-copy decoding: fields (type, chain ID, sender, recipient, value, nonce, gas limit, signature, access list) appear in a fixed order, variable-length fields carry a one-byte length prefix, contract creation is signaled by a marker byte, and all remaining bytes are the calldata. A parser reads each transaction in one pass with no allocation-heavy tree construction, which matters when decoding hundreds of thousands of transactions per second.

​
EVM compatibility

Sei Giga’s EVM will be mostly equivalent to mainnet Ethereum. Contracts will be written in standard Solidity or Vyper and deployed with standard tooling.

​
Fee model

​
Storage

Giga’s storage layer is designed for petabyte-per-year data production at full 5-gigagas load while keeping validator hardware practical.

​
Flat state, RAM-first

  • Every account, storage slot, and global variable will map directly to an entry in a log-structured merge (LSM) tree. Writes will skip per-write Merkle path updates entirely, so flushes stay batched and sequential and nothing is re-hashed on the write path.
  • Frequently accessed state will be held in RAM, and reads will be served from memory in the common case. All disk writes will be asynchronous and exist for durability only, protected by an append-only write-ahead log (WAL) that is replayed on crash recovery.
  • Storage will be tiered: recent and hot data will sit on local high-performance SSDs, while historical data will move to a distributed columnar store built for analytical queries and audit workloads.

​
Lattice-hash divergence digests

There will be no state root; Giga will instead commit to execution results with a homomorphic multiset hash (LtHash, by Lewi, Kim, Maykov, and Weis): LH(X) = Σ h(x) mod q. Its collision resistance rests on lattice assumptions (short integer solution style). For each block n:
  • The committed multiset X_n will contain one record per surviving write (after intra-block last-write-wins resolution), one record per transaction receipt (position-bound), and one gas-accounting record, each domain-separated by type tag and height.
  • The block digest is d_n = LH(X_n); validators will attest to the compact commitment D_n = H(enc(n, d_n)). The full vector d_n will be exchanged only during disputes.
  • Disputes will resolve by bisection. The key space partitions into ranges whose chunk digests sum to the write component of d_n by construction, so divergent executors will compare chunk digests, narrow down, and replay only the affected range to find the first divergent write, receipt, or gas discrepancy.
The homomorphism is what makes this practical: digests update incrementally as writes commit, in any order, and no tree walk is involved.

​
Block Update Digests (BUDs)

BUDs will restore externally verifiable state proofs (the role eth_getProof plays on Ethereum) at a cost proportional to per-block update volume rather than total state size:
  • Every state entry will carry an 8-byte last-modified height and a 1-byte serialization version. For each block n, the BUD U_n is the Merkle root over the lexicographically sorted leaves (key, newValue, n, prevHeight) of that block’s writes. Validators will attest U_n on the same delayed 2/3-quorum schedule as the divergence digest.
  • A membership proof will be a Merkle path to an attested U_n, certifying that key held value immediately after block n and recording when it previously changed. Two proofs at heights a < b whose b-leaf records predecessor a will prove the key was unmodified throughout (a, b).
  • SuperBUDs will aggregate BUDs over exponentially growing aligned windows (branching base e and maximum level L_max, both governance parameters), so provers will cover long ranges with logarithmically many digests. The guaranteed proof window will be η = e^L_max blocks; older claims can be served by archive nodes but fall outside the protocol guarantee.
  • Touch transactions will rewrite only a key’s last-modified metadata, giving long-untouched keys a fresh proof anchor. Deletions will leave tombstones, garbage-collected after η, which anchor exclusion proofs.
  • At the activation height a one-time synthetic write log will bootstrap every existing key, and the system will reach steady state after η blocks. BUD trees deliberately use a classical hash: the short proof window keeps classical collision resistance sufficient, and the trees will fall under the same post-quantum migration schedule as the rest of the protocol.
Light clients, bridges, and any external verifier will consume BUD proofs against attested digests instead of Merkle-Patricia proofs against a state root.

​
Networking and transaction ingress

  • Nodes will communicate over direct, authenticated point-to-point connections; nothing will be gossip-flooded. Consensus messages, lane proposals, votes, and certificates will stream over dedicated channels with per-channel rate and size limits.
  • There will be no traditional public mempool. Transactions will route through Sedna, Giga’s private dissemination layer, into validator lanes for immediate inclusion, allocated by stake weight. In the current implementation, EVM senders map deterministically to a validator shard, and eth_sendRawTransaction plus pending-nonce queries are proxied to that shard’s owner.
  • Users will be able to submit the same transaction to multiple validators for censorship resistance. Admission will be rate-limited: each validator will include at most one copy of a given transaction per epoch, duplicates will be dropped deterministically at merge time, only one copy will execute, and unexecuted duplicates will earn a partial tip refund while paying the distribution fee.
  • Four node roles will exist: validators (consensus and execution), full nodes (RPC plus execution for the read path), light nodes (RPC only), and data nodes that serve recent data.

​
Sedna: private dissemination

Sedna will be Giga’s private dissemination layer, the mempool-adjacent stage of the transaction path: transactions will route through Sedna on their way into validator lanes. Senders will encode a committed transaction payload into verifiable rateless coded symbols and send addressed bundles to selected proposer lanes. No lane will see the whole transaction, and executors will reconstruct the unique payload only after ordering, once finalized symbols cross the decode threshold (“until-decode privacy”). Compared with threshold-encrypted mempools, the Sedna paper argues this design reaches similar pre-execution privacy without an extra decryption round or any trust assumption beyond the existing f + 1 availability quorum, and with better goodput; coding is also designed to cut per-lane bandwidth to a fraction of the payload size. The companion incentive mechanism PIVOT-K will concentrate a sender-funded bounty on the bundles that trigger decoding and ratchet away from lanes that withhold, a mechanism designed to close the withholding attack. Sedna will ship as its own roadmap milestone after Autobahn reaches mainnet.

​
MEV and fee design

Multi-Proposer architectures remove the single block-builder’s private ordering monopoly but introduce their own MEV (maximal extractable value) channels, formalized in MEV in Multiple Concurrent Proposer Blockchains: same-tick duplicate stealing (copying a visible transaction into your own lane to win the merge), proposer-to-proposer orderflow deals, and timing races around PoA latency. Giga’s countermeasures will live at the protocol level.

​
Deterministic merge rule

For each committed cut, every node will derive the executable sequence with the same pure function:
  1. Take each lane’s newly committed transactions, meaning those not in any previous cut, in their intra-lane order.
  2. Sort lanes by the maximum priority fee among their new transactions, descending; break ties by replica index.
  3. Concatenate the lanes and deduplicate by transaction hash; only the first occurrence survives.
The merged order will depend only on finalized lane contents, not on arrival timing, wall clocks, or any node’s discretion — a design that leaves no post-consensus ordering game to play.

​
Socialised tips

All priority fees collected in an epoch (net of duplicate refunds) will be pooled and distributed to validators pro rata by stake × liveness, where liveness will be the measured fraction of observable duties performed: consensus votes included in committed QCs, certified lane blocks produced, and signed state attestations, with duty weighting set by governance. Payouts will be shared with delegators in the same way as block rewards.
  • Copying a high-tip transaction into your own lane will not capture its fee, a design that removes the duplicate-steal channel’s revenue motive.
  • Validator revenue will be independent of orderflow routing, removing the protocol-level incentive to steer users to specific proposers.
  • Withholding or lazy participation will directly reduce a validator’s payout.
The whitepaper sums it up: the priority fee will buy ordering, not a relationship with a particular proposer. Side payments for intra-lane position are out of protocol scope for now and belong to the forthcoming fee-mechanism work.

​
Post-quantum migration

Giga will ship with a survivability path for a sudden ECDSA break (“Q-day”) that avoids a chain-wide account reset:
  • Before a governance-set cutoff height, any account will be able to register a post-quantum verification key (scheme identifier, PQ public key, migration nonce, optional activation height), signed with its current classical key.
  • During the transition window the chain will accept classical or dual classical+PQ signatures. After the cutoff, verification will be table-driven PQ-only: unregistered accounts will become invalid, there will be no public-key-recovery path, and no new classical EOAs will be creatable. Onboarding will continue through pre-registration, contract wallets, or a later native PQ account format.
  • The designated short-term scheme is ML-DSA (FIPS 204). The whitepaper is explicit that this is an emergency path and not fast enough for Giga’s throughput; post-quantum cryptography at Giga scale is open research.

​
Performance

The whitepaper publishes no fixed block gas limit, block size, or validator hardware specification for Giga; the roadmap’s Autobahn testnet milestone includes the final consensus specification. Figures you may see for today’s network (block times, gas limits) describe the current architecture, not Giga.

​
Implementation snapshot (sei-chain v6.6 release line, July 2026)

Giga is implemented in the open in sei-protocol/sei-chain; there is no separate Giga repository. The facts below describe the v6.6 release line and can change before network activation: Node operators should follow the node configuration reference rather than this page for exact keys and defaults.

​
Glossary

​
References

Last updated July 2026, based on the Giga whitepaper v2.0 (June 29, 2026) and the sei-chain v6.6 release line.