What is Thunder?
Thunder is a drivechain on eCash (ECX) built for one job: making everyday payments work at global scale. It uses large, prunable blocks and fraud proofs, and it pays transaction fees to the same miners who secure the base layer.
There are no payment channels, no inbound liquidity to manage, and no failed routes. You send a payment and it confirms.
Thunder isn't really one chain. Paul Sztorc designed it as a family of large-block sidechains — he calls each one a "T-network" — added in parallel as demand grows, partitioned by region the way phone systems and banking networks already are.
Thunder at a glance
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Drivechain (BIP 300/301 sidechain) on eCash
Type
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High-throughput payments
Purpose
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Built by LayerTwo Labs
Built by
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ECX (no separate token)
Native coin
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Large blocks, prunable history, fraud proofs
Key design
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Designed to start around 10 MB and rise toward 1 GB over roughly ten years
Block size
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Two-way, secured by Bitcoin miners
Peg
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github.com/LayerTwo-Labs/thunder-rust
Repository
Canonical writeup
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truthcoin.info/blog/thunder/ (Paul Sztorc, Feb 2021)
The problem Thunder solves
Bitcoin's base layer handles a few transactions per second. That's deliberate — small blocks keep the cost of running a node low, which keeps the network decentralized. It also means Bitcoin can't be the money people spend day to day.
The usual answer is Lightning. Lightning barely works because it asks users to manage channels, inbound liquidity, and routing, and payments can fail for reasons a normal user can't diagnose. It also moves fee revenue away from miners.
Thunder takes the other road: a separate chain with big blocks, where the base layer stays small and the miners still get paid.
How Thunder works
1. Peg in. You move ECX from the eCash main chain to Thunder through the BIP 300 two-way peg. No custodian holds it.
2.Transact. Thunder's blocks are large, so fees stay low and capacity is high. Payments confirm on-chain, so there's no channel state to manage.
3. Stay light. Thunder is prunable — nodes don't have to store the full history forever, which is what keeps a big-block chain runnable by ordinary users.
4. Peg out. Withdrawals return to the main chain through miner-voted bundles over the 13,000-block window.
Why prunable matters
A 1 GB block every ten minutes is about 26 terabytes of block data every six months. Thunder's answer is that sidechains, unlike the main chain, can discard old history — with UTXO commitments, potentially everything older than about six months. That's what keeps a big-block chain runnable by someone other than a data center.
Fraud proofs
On a large-block chain, most people will run light (SPV) nodes rather than full ones. Normally that means trusting that blocks are valid. Thunder's design uses accumulators to make invalid blocks provable, so a light node can be warned cheaply and immediately if any block is bad — closing most of the security gap between light and full nodes. Paul is careful about the limit here, and you should be too: fraud proofs don't remove the data availability problem. Someone still has to host the data. Not everyone can get it from someone else
Thunder vs Lightning vs Custodial
Paul frames Thunder against two rivals, not one: Lightning and plain custodial wallets. That's the more honest comparison, because custodial services are what most people actually use.
Thunder
Lightning
Custodial
Peg in and send.
Requires layer-1 block space for every new user.
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