# A Guide to Building Bitcoin Applications on Citrea I Talip Akalin

- Channel: [ETHGlobal](https://streameth.org/ethglobal)
- Date: 2025-11-09
- Duration: 19:12
- Topics: Citrea, Bitcoin L2, ZK rollup, RISC-Zero ZKVM, validity proofs, data availability on Bitcoin, BTC as native gas, EVM-compatible, Solidity on Bitcoin, BitVM, trust-minimized bridge, Clementine bridge, challenge game, multisig risks, one-honest-party assumption, DeFi on Bitcoin, DEX, lending, stablecoin, prediction markets, offline BTC payments, hyperbitcoinization, Citrea Origins, hackathon tracks, open innovation
- Watch: https://streameth.org/watch/yt-SSYqsfljXYY
- YouTube: https://www.youtube.com/watch?v=SSYqsfljXYY

## Description

Talip Akalın introduces Citrea, an EVM-compatible ZK rollup that brings full smart-contract functionality to Bitcoin without changing L1. He frames Bitcoin’s limitations (Script’s low expressivity, fee spikes, slow upgrades) and the risks of today’s BTC bridges (multisig/“honest majority” custody). Citrea’s architecture: a sequencer produces L2 blocks, validity proofs (RISC-Zero ZKVM) attest to state, and data is published on Bitcoin, letting users treat Bitcoin as the single source of truth. BTC is the native gas/asset on Citrea, so existing Solidity apps (DEXs, lending, etc.) can be “forked” to work with real BTC rather than wrapped derivatives.

The bridge design (“Clementine”) uses BitVM-based challenge games plus ZK proofs to kick out malicious signers, shifting the assumption from “honest majority” to “at least one honest participant,” a stronger trust model than typical multisig bridges. For the hackathon, Citrea offers two tracks—Open Innovation (any novel app using BTC on Citrea) and DeFi (fork/improve core money apps). Beyond the weekend, the Citrea Origins builder program provides mentorship, go-to-market, fundraising, and hiring support; early teams include wallets, a BTC-backed stablecoin, a native DEX, money markets, prediction markets, and offline SMS Bitcoin payments. The aim: catalyze a BTC-centric alternative economy (“hyperbitcoinization”) by making Bitcoin practical for rich onchain applications.

00:02 – Intro, talk scope & hackathon focus
02:04 – Why Bitcoin matters beyond price; limitations in practice
03:51 – Script vs Solidity; fees, capacity, and upgrade constraints
05:28 – Using other layers: wrapped BTC & bridge risks
07:55 – The bridge problem (multisig custody, exploits)
08:19 – What is Citrea: EVM rollup secured by Bitcoin + ZK proofs
09:12 – BTC as native asset; build DeFi/apps with real BTC
09:46 – Why Citrea’s bridge is different: BitVM + ZK challenges
10:39 – Trust model shift: “one honest party” vs “honest majority”
12:47 – Testnet, funding, partners, readiness
13:53 – Hackathon tracks: Open Innovation & DeFi
15:01 – Vision: hyperbitcoinization & BTC-centric economy
16:33 – Citrea Origins: builder community & support
18:37 – Hacker houses, testimonials, call to join

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🇮🇳 *ETHGlobal New Delhi*
This workshop is specifically for ETHGlobal New Delhi, a 3-day hackathon held September 19-21 at the India International Convention & Expo Centre, bringing together the most skilled web3 developers, designers and product builders from all around the globe for a weekend-long adventure to advance the Ethereum ecosystem! Watch the full ETHGlobal New Delhi 2025 playlist here: https://www.youtube.com/playlist?list=PLXzKMXK2aHh7zCFW3hBqatZ18rQaYeEJL
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