# OffchainLabs/arbitrum-classic

Powers fast, private, decentralized applications

Repository: https://github.com/OffchainLabs/arbitrum-classic
Canonical: https://ross.abutalabs.com/products/arbitrum-classic
Homepage: https://offchainlabs.com/
Language: Go
License: Apache-2.0
License Family: permissive
Last push: 2026-03-03T15:38:05+00:00

## Health v2 (maintenance only)
Score: 57/100 (v2, computed 2026-09-03T02:20:16.233290+00:00)
- activity 70, release rhythm 16, longevity 100
- inputs: {"age_days": 2585, "days_push": 183, "days_rel": 351, "gap_med": null, "n_releases_24m": 1}
- flags: none
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 1999, forks 1401 (observed 2026-08-28T04:06:03.779145+00:00)

## What it is
Arbitrum Classic is the original Arbitrum Layer-2 optimistic rollup tech stack for Ethereum, implemented in Go, that powers fast and private decentralized applications. It is a legacy monorepo, as Arbitrum One was upgraded to the Nitro stack in August 2022.

## Use cases
- run a legacy Arbitrum Classic node
- build dapps on the original Arbitrum rollup
- study the pre-Nitro Arbitrum validator and sequencer implementation
- maintain or migrate an app still on the classic Arbitrum stack
- research optimistic rollup execution in Go

## When to choose
- you must operate or audit the legacy Arbitrum Classic chain
- you need to reference the original rollup implementation for research or migration

## When to avoid
- you are building a new dapp or node on Arbitrum - use the Nitro codebase instead
- you want an actively developed Layer-2 stack

## Facets
- artifact type: application
- maturity: maintenance
- function: blockchain, rpc, developer-tools
- domain: blockchain, developer-tools, microservices
- platform: windows, go, cross-platform
- tags: ethereum, layer-2, optimistic-rollup, arbitrum, smart-contracts, monorepo, legacy, deprecated-in-favor-of-nitro, virtual-machine, cryptocurrency, linux, macos

## Member repositories
- OffchainLabs/arbitrum-classic (main) score 57

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:06:03.779145+00:00.
- Health v2: computed from the inputs above; adoption is never an input.
- Inferred fields (summary, facets, guidance): AI-extracted, prompt v1, taxonomy v1, on 2026-08-30T03:02:09.842233+00:00, confidence not recorded.
  - readme: https://github.com/OffchainLabs/arbitrum-classic (fetched 2026-08-28T04:06:03.779145+00:00, sha 11257a716aba)
  - homepage: https://offchainlabs.com/ (fetched 2026-08-29T10:41:52.523757+00:00, sha 8076c31383b2)
  - site_page: https://www.offchain.io/blog/research/debunking-common-misconceptions-about-timeboost (fetched 2026-08-29T10:41:52.532916+00:00, sha 8049a4a24c7e)
- Data as of 2026-08-30T08:39:29.467469+00:00.