Bitcoin Layer 2 Explained: Lightning, Sidechains and Rollups

Last updated: October 26, 2026. Market data as of October 26, 2026; dollar values use bitcoin’s October 25, 2026 close of $80,053.

Short answer: A bitcoin layer 2 (often called a bitcoin L2) is a separate system built on top of the bitcoin blockchain to make payments faster and cheaper. The main one is the Lightning Network, which moves bitcoin through payment channels for about a cent on a $100 payment. Others, like Liquid, Rootstock and Stacks, are separate chains where a group of signers holds the real bitcoin. Newer rollups like Citrea use a bridge (the system that holds your real bitcoin) that needs only one honest participant. Before you use any of them, ask one question: if the operator disappears, can you get your bitcoin back on your own?

Key takeaways

• Why layer 2s exist: bitcoin adds a block about every 10 minutes and handles only a few transactions per second.
• Lightning is the main payment layer: 2,571 BTC in public channels and 15,255 nodes on October 21, 2026, per mempool.space, down about 38% in a year. A typical routing fee is 0.01% of the payment per hop.
• Most other “layer 2s” rely on signers: Liquid’s bitcoin is controlled by 11 of 15 signers, and Stacks’ sBTC by 15 signers with a 70% threshold.
• It has gone wrong: on September 6, 2026, a software bug let an attacker pull about 4,000 BTC (about $320 million) out of Liquid’s bridge. About 3,400 BTC came back; roughly 600 BTC is still missing, and Liquid’s own withdrawals to bitcoin are still restricted.
• Fees on bitcoin itself are low right now: about $0.11 to $0.56 for a simple transaction on October 26, 2026.

What is a bitcoin layer 2?

Layer 1 is the bitcoin blockchain itself. A layer 2 is anything built on top of it that handles transactions somewhere else and settles back to bitcoin. You’ll also see it written as “bitcoin L2.”

Bitcoin’s base layer is slow by design. A new block arrives about every 10 minutes. Each block has limited space, which works out to single-digit transactions per second. That keeps the network easy to verify, but it can’t handle millions of coffee purchases.

When demand spikes, fees jump. On April 20, 2024, the halving block (block 840,000) paid about 37.6 BTC in fees, just over $2.4 million, across 3,050 transactions. That was an extreme case, driven by the launch of Runes tokens. The average fee that whole day hit a record $128, Cointelegraph reported.

Right now it’s calm. On October 26, 2026, mempool.space recommended 1 to 5 sat/vB. A satoshi (“sat”) is 0.00000001 BTC, and a vB (virtual byte) measures transaction size. A simple payment is about 140 vB, so it costs about $0.11 to $0.56. Using a newer address type helps too: SegWit and Taproot addresses make transactions smaller, as our guide to bitcoin address formats explains.

What this means for you: if you send bitcoin once a month, layer 1 is fine. If you want to pay for small things often, or fees spike again, a layer 2 saves money.

The three main types

Type	Example	Who holds your BTC	Can you exit alone?
Payment channels	Lightning	You, in a self-custody wallet	Yes
Sidechain	Liquid, Rootstock, Stacks	A group of signers	No
Rollup with a BitVM bridge	Citrea	A bridge that needs one honest participant	Yes, but the design is new

How the Lightning Network works

Lightning lets two people lock bitcoin into a shared wallet (a channel) and then trade balances back and forth instantly, without writing each payment to the blockchain.

Here’s the basic flow:

1. You open a channel with an on-chain transaction, for example locking 0.01 BTC.
2. Inside the channel, you and the other side sign new balances for each payment. Nothing goes on-chain.
3. Payments can hop through other channels to reach someone you don’t have a channel with.
4. When you’re done, you close the channel and the final balance settles on bitcoin.

The key safety feature: you can always close the channel on your own and get your bitcoin back on-chain. If the other side tries to cheat with an old balance, the protocol lets you take their funds as a penalty. That works only if your wallet, or a watchtower service watching for you, spots it in time.

Lightning by the numbers

Measure	Value	Date
Public capacity	2,570.50 BTC (about $206 million)	October 21, 2026
A year earlier	4,123.21 BTC	October 27, 2025
Peak capacity	about 5,600 BTC	December 2025
Public nodes	15,255	October 21, 2026
Public channels	25,211	October 21, 2026
Median routing fee, per hop	100 ppm (parts per million, or 0.01%) plus 0.5 sat	October 21, 2026
Monthly volume	$1.17 billion	November 2025

Public capacity counts only announced channels; private channels aren’t included. The peak is Spark Research’s figure, and monthly volume is from River’s report. Dollar value at $80,053 per BTC, the October 25, 2026 close.

Public capacity fell about 38% in a year, from 4,123 BTC on October 27, 2025 to 2,571 BTC on October 21, 2026, per mempool.space. That’s more than half below the December 2025 peak. Most of the drop came this summer: capacity was 4,789 BTC on June 18, 2026 and 2,433 BTC on August 27, 2026. 1ML, which counts differently, showed a similar 2,454 BTC on October 26, 2026. Meanwhile, large apps have added it: by mid-2025, more than 15% of bitcoin withdrawals from Coinbase used Lightning, per Spark Research. Cash App routes about 1 in 4 of its bitcoin payments over it, per SpendNode.

Worked example: you pay $100 over Lightning through one hop at the median fee of 100 ppm plus 0.5 sat. The fee is about $0.01 plus a fraction of a cent. Each extra hop adds a similar fee. The same payment on-chain cost $0.11 to $0.56 on October 26, 2026.

Lightning’s limits

• Custodial apps: many popular Lightning apps, including exchange apps, are custodial. The company holds the bitcoin, not you.
• Liquidity: to receive money, someone must have funds on your side of a channel. Most wallets handle this for you, for a fee.
• Online requirement: a self-custody Lightning wallet needs to be online to receive payments.
• Closing costs: a forced channel close needs an on-chain transaction and can lock funds for days, sometimes up to two weeks.
• A few big hubs: the top 10 nodes control about 85% of public capacity, per River’s analysis as reported by SpendNode in February 2026.
• Hot wallets: Lightning funds sit on internet-connected nodes. In August 2026, attackers stole merchant funds from Lightning nodes set up with BTCPay Server. We covered the BTCPay Server Lightning exploit. That was a server security failure, not a break in Lightning itself.

Watch out: the “close your channel and walk away” safety only applies to self-custody Lightning wallets. In a custodial app, you’re trusting the company.

Bitcoin sidechains: Liquid, Rootstock and Stacks

A sidechain is a separate blockchain. You send bitcoin to a bridge, and you get a token on the sidechain that’s supposed to be worth 1 BTC. The real bitcoin sits in a wallet controlled by a group of signers. You trust that group.

Network	What it does	Who holds the real BTC	Size (date)
Liquid (Blockstream)	Fast transfers between exchanges and traders, confidential amounts	11 of 15 signers (federation)	4,235 L-BTC backed by 3,632 BTC (October 21, 2026)
Rootstock	Smart contracts; miners with 84% of bitcoin’s mining power also mine it (Q2 2026)	A group of signers using special hardware (PowPeg)	$74.9 million in apps (October 26, 2026)
Stacks	Smart contracts, sBTC token	15 signers, 70% threshold	$61.6 million in apps (October 26, 2026)

For Rootstock and Stacks, size is money in apps on each chain (DefiLlama, October 26, 2026), not all bitcoin bridged to it.

Watch out: merged mining sounds like bitcoin-level security. On Rootstock, it protects the blocks and adds a check on withdrawals, because the signing hardware follows only the chain with the most work. But the bitcoin itself still sits in a multisig run by a small, fixed group, so you are still trusting them.

What happened to Liquid in September 2026

On September 6, 2026, an attacker used a bug in Liquid’s software to create about 4,000 unbacked L-BTC and redeem them for real bitcoin, about $320 million. Ledger’s CTO questioned the attacker’s “whitehat” claim. About 3,400 BTC came back the next day. Roughly 598.5 BTC did not.

As of October 21, 2026, reserves were 3,632 BTC against 4,235 L-BTC in circulation, about 603 BTC (14%) short. Direct withdrawals to bitcoin through the federation (peg-outs) are still restricted, with no restart date. The federation says it will restore full backing first. Here’s our report on the Liquid reserve gap.

There is now a way out, but it isn’t the bridge. On October 20, 2026, the SideSwap service started swapping L-BTC for BTC at 1:1 minus a 0.1% fee, paid from its own bitcoin wallet. By October 21 it had handled about 600 swaps worth more than 60 BTC. Big requests wait in a queue until SideSwap refills its wallet, and the swaps don’t close the reserve gap.

No signer keys were stolen. The bug was in the software that checks transactions. That’s the point: a bridge can fail even when the signers do everything right.

What this means for you: on a sidechain, your “bitcoin” is an IOU. If the bridge freezes, you may not be able to turn it back into BTC for weeks.

Rollups and the newest designs

A rollup bundles many transactions off-chain and posts proof of them to bitcoin. The hard part on bitcoin is the bridge, because bitcoin can’t check those proofs directly today.

• Citrea launched its mainnet on January 27, 2026. Its bridge uses BitVM, a method where only one honest participant among the bridge’s operators is needed to stop a bad withdrawal. That’s a big step up from trusting a majority of signers, but it’s new and lightly tested. Value locked: $9.1 million on October 26, 2026.
• Ark lets many users share one on-chain bitcoin transaction. An operator coordinates, but you can exit on-chain on your own, as long as you come online before your coins’ expiry. Ark Labs opened a public beta on October 21, 2025.
• Spark works like a statechain. You and an operator share the keys to a coin, and when the coin changes hands the operator is supposed to delete its old key. You can exit on your own, but you trust that at least one operator really deleted those old keys. It runs with two operators, Lightspark and Flashnet, according to Spark’s own docs (checked October 20, 2026).
• Ethereum-style “bitcoin L2s” (EVM chains) like BOB and Merlin run their own bridges. Their trust setups vary, so check each one.

Babylon is not a layer 2. It lets you stake bitcoin to secure other networks while the BTC stays on bitcoin in a time-locked script. It held $3.28 billion on October 26, 2026, per DefiLlama, down from about $6.38 billion a year earlier.