# \[CONSTITUTIONAL\] AIP: ArbOS Version 40 Callisto
**URL:** https://forum.arbitrum.foundation/t/constitutional-aip-arbos-version-40-callisto/28436
**Category:** Finalized AIPs
**Created:** [February 13, 2025, 1:55pm UTC](https://forum.arbitrum.foundation/t/constitutional-aip-arbos-version-40-callisto/28436 "2025-02-13T13:55:57Z")
**Posts on this page:** 20
**Page:** 3
### Author:  [@Arbitrum](https://forum.arbitrum.foundation/u/Arbitrum)
#### Post date: [March 13, 2025, 9:19am UTC](https://forum.arbitrum.foundation/t/constitutional-aip-arbos-version-40-callisto/28436/41 "2025-03-13T09:19:47Z")
> [@\[CONSTITUTIONAL\] AIP: ArbOS Version 40 Callisto](https://forum.arbitrum.foundation/t/constitutional-aip-arbos-version-40-callisto/28436/3):
>
> Glad to see the proposal to support Pectra! When is the snapshot estimated for? Also, could there be any issues in the future with not adopting 7623 and having different calldata costs?
- The [Snapshot vote](https://snapshot.box/#/s:arbitrumfoundation.eth/proposal/0x7cc26491a070c74c1a4ec5a9892571d31eb690015936a35b52c0d3a97bd5497f) has already been posted and has passed successfully at the time of writing. Not adopting EIP-7623 initially will change how Arbitrum chains calculate gas costs for calldata-heavy transactions, compared to L1, but will otherwise not alter how gas is estimated and charged to the user at the application layer. Operations and use cases that rely on calldata-heavy transactions will have their gas costs calculated the same way as it is done today, pre-Pectra.
> [@\[CONSTITUTIONAL\] AIP: ArbOS Version 40 Callisto](https://forum.arbitrum.foundation/t/constitutional-aip-arbos-version-40-callisto/28436/6):
>
> Good and detailed description of the changes, and useful rationale for the EIPs that will not be applied. I have a question about the update date. Can something not work correctly in Arbitrum if the Ethereum network is already updated, but Arbitrum is not?
- Yes it is possible. Nitro node version 3.5.3 and nitro-contracts 3.0.0 or 2.1.3 should be used for chains settling to a Pectra-enabled Ethereum chain (like Sepolia or Holesky). Should this vote pass, a new Nitro version with ArbOS 40 will be released for Arbitrum one and Arbitrum nova node operators to use as a mandatory upgrade.
> [@\[CONSTITUTIONAL\] AIP: ArbOS Version 40 Callisto](https://forum.arbitrum.foundation/t/constitutional-aip-arbos-version-40-callisto/28436/7):
>
> Overall, the Callisto upgrade appears to be a substantial step forward for Arbitrum in keeping up with Ethereum’s roadmap and we are in favour of it. Our only question @Arbitrum is whether developer tooling gaps and overall readiness have been accounted for to ensure a smooth transition amongst Arbitrum builders.
- Yes - Arbitrum builders across protocols and developer tooling have been consulted in anticipation for this upgrade on Pectra. This includes Orbit chain owners and Rollup-as-a-Service (RaaS) teams who may need to apply a small patch to ensure their chains are compatible with a parent chain that has upgraded to use Pectra.
> [@\[CONSTITUTIONAL\] AIP: ArbOS Version 40 Callisto](https://forum.arbitrum.foundation/t/constitutional-aip-arbos-version-40-callisto/28436/8):
>
> Hello! Thanks for this exciting news! I have a few questions: About the process itself, can you clarify the difference between steps 2 and 6? I’m assuming this is the same vote (step 2), correct? And the steps 3-6 will follow that. About the timeline Do you have an update regarding the releases that were supposed to happen on Feb 13th? This sentence: “there is a strong likelihood that ArbOS 40 Callisto will be activated on Arbitrum One and Arbitrum Nova after Ethereum Mainnet upgrades to …
- Yes - Step 6 is the formal deployment of a release candidate of the Nitro node software that supports Pectra, while Step 2 is the temperature check vote held on Snapshot.
- It is our understanding that client teams have already released their Pectra-supported versions for Ethereum Holesky, including Geth’s 1.15.0 release. We strongly recommend following Ethereum Core Development discussions on [https://ethereum-magicians.org/](https://ethereum-magicians.org/) and in their respective All Core Devs call, rather than this forum post.
- This is meant to be an informative message.
> [@\[CONSTITUTIONAL\] AIP: ArbOS Version 40 Callisto](https://forum.arbitrum.foundation/t/constitutional-aip-arbos-version-40-callisto/28436/21):
>
> We vote FOR the proposal on Snapshot. We have reviewed EIPs to be included (and not included) in the Callisto upgrade and we find the rationale behind each decision clear and articulated. We are particularly excited about the EIP-7702 change to be included on Arbitrum One and Nova for users on those chains as we believe the change will drastically improve the user experience over time. We have a couple of questions: Even reading [the detailed document](https://docs.arbitrum.io/launch-orbit-chain/configure-your-chain/common-configurations/arbos-upgrade#step-3-schedule-the-arbos-version-upgrade), it wasn’t clear what the “technical deta…
- These changes refer to modifications that Orbit chains may want to make to ArbOS and to prevent versioning collisions between their modifications and official ArbOS releases. For example, if an Orbit chain wanted to modify ArbOS 40 and release their modifications as ArbOS 41, then the official Offchain Labs ArbOS release versions would not conflict since the next official version would be ArbOS 50.
- With any upgrade to the Arbitrum tech stack (including ArbOS 20 for Ethereum’s Dencun upgrade in March 2024), Orbit chains have full discretion over what ArbOS version to use for their chain and what customizations they want to make. We generally recommend Orbit chains upgrade to a new ArbOS release approximately 30 days after the release has been in production on Arbitrum One or Arbitrum Nova (pending governance).
> [@\[CONSTITUTIONAL\] AIP: ArbOS Version 40 Callisto](https://forum.arbitrum.foundation/t/constitutional-aip-arbos-version-40-callisto/28436/30):
>
> voting Abstain on the current offchain vote because I have no idea of the risks this upgrade will entail without seeing the results of an independent audit to the smart contract code. And I also think the governance process for this proposal has not been followed in the best way it could. I think the Arbitrum DAO delegates should be asked to vote, even on a temperature check, in as much of a fully fleshed out proposal, as possible. This proposal is not ready to be voted on by delegates, in my op…
- As defined in the [ArbitrumDAO’s Constitution](https://docs.arbitrum.foundation/dao-constitution#section-2-dao-proposals-and-voting-procedures), a temperature check vote is optional and is considered a matter of good governance practice. Furthermore, in the Steps to Implement section, there are clear steps that follow after the temperature check that a security audit by Trail of Bits is underway, and that a public report will be ready by the time this proposal is submitted to Tally for a formal on-chain vote. The vote here is to signal the readiness of the DAO to have this upgrade ready on both private devnets and Arbitrum Sepolia for further testing.
---
### Author:  [@Tane](https://forum.arbitrum.foundation/u/Tane)
#### Post date: [March 19, 2025, 5:18am UTC](https://forum.arbitrum.foundation/t/constitutional-aip-arbos-version-40-callisto/28436/42 "2025-03-19T05:18:36Z")
Thanks for the detailed clarifications.
> [@Arbitrum](#):
>
> if an Orbit chain wanted to modify ArbOS 40 and release their modifications as ArbOS 41, then the official Offchain Labs ArbOS release versions would not conflict since the next official version would be ArbOS 50.
Makes sense! Have you considered introducing the minor versions to the ArbOS like [the semantic versioning](https://semver.org/)? We think it’s cleaner.
> [@Arbitrum](#):
>
> We generally recommend Orbit chains upgrade to a new ArbOS release approximately 30 days after the release has been in production on Arbitrum One or Arbitrum Nova
Great to know! It would be great to be clarified in the documentation as well.
---
### Author:  [@Arbitrum](https://forum.arbitrum.foundation/u/Arbitrum)
#### Post date: [April 24, 2025, 1:06pm UTC](https://forum.arbitrum.foundation/t/constitutional-aip-arbos-version-40-callisto/28436/43 "2025-04-24T13:06:43Z")
Hello! We’re preparing to propose an upgrade to the Arbitrum Nitro stack to support Ethereum’s upcoming [Pectra hard fork](https://eips.ethereum.org/EIPS/eip-7600), via **ArbOS 40 Callisto** and wanted to give our ecosystem partners and the ArbitrumDAO a status update. Please refer to the original AIP forum post above, for details.
At the time of writing, the proposal to bring Pectra’s changes to Arbitrum via ArbOS 40 has already passed a [temperature check vote on Snapshot](https://snapshot.box/#/s:arbitrumfoundation.eth/proposal/0x7cc26491a070c74c1a4ec5a9892571d31eb690015936a35b52c0d3a97bd5497f) and a security audit has recently wrapped up.
Below are a few critical dates, around what will happen next, that we wanted to communicate with the ecosystem:
- **May 5, 2025: ArbOS 40 Callisto will activate on Arbitrum Sepolia**
- Arbitrum Sepolia node operators must upgrade to the soon-to-be released Nitro v3.6.x ahead of this date to continue syncing the chain. A follow-up message will be circulated via social channels and Arbitrum documentation when this release is ready.
- **May 12, 2025: ArbOS 40 Callisto Tally Proposal for Arbitrum One and Arbitrum Nova**
- The formal constitutional on-chain proposal to activate ArbOS 40 on Arbitrum One and Arbitrum Nova is scheduled to be posted on May 12, to commence on May 15.
- **Mid-June, 2025: ArbOS 40 Callisto will be activated on Arbitrum One and Arbitrum Nova, assuming the ArbitrumDAO passes the proposal.**
- Node operators (for Arbitrum One and Arbitrum Nova) will be asked to upgrade their Nitro nodes to the soon-to-be-released version that supports ArbOS 40. A follow-up message will be circulated via social channels and Arbitrum documentation when this release is ready.
- **Mid-July, 2025: ArbOS 40 Callisto will be formally supported for Arbitrum Orbit chain owners and operators.**
- Action will be required for Node Operators to upgrade both their chains’ Arbitrum Nitro nodes and rollup contracts. Further documentation, instructions, and release notes for how to do this will be shared.
Further documentation, upgrade instructions, and release notes for Nitro v3.6.x will be shared shortly. Node operators should ensure that their infrastructure is prepared for the Arbitrum Sepolia upgrade.
We recommend subscribing to [Telegram: View @arbitrumnodeupgrade](https://t.me/arbitrumnodeupgrade) for regular updates about upgrade notices like this.
---
### Author:  [@WinVerse](https://forum.arbitrum.foundation/u/WinVerse)
#### Post date: [May 15, 2025, 8:11pm UTC](https://forum.arbitrum.foundation/t/constitutional-aip-arbos-version-40-callisto/28436/44 "2025-05-15T20:11:40Z")
DAOplomats voted FOR this proposal on Tally.
We originally supported this constitutional proposal to activate ArbOS 40 during the temp check. Also, with the positive conclusion of the security audit, we were confident in supporting the proposal during the onchain vote.
---
### Author:  [@paulofonseca](https://forum.arbitrum.foundation/u/paulofonseca)
#### Post date: [May 15, 2025, 8:56pm UTC](https://forum.arbitrum.foundation/t/constitutional-aip-arbos-version-40-callisto/28436/45 "2025-05-15T20:56:45Z")
> [@Arbitrum](#):
>
> and a security audit has recently wrapped up.
@arbitrum or @offchain where can we see this security audit?
delegates should only vote on this major onchain proposal after seeing the security audit output, right?
---
### Author:  [@lobbyfi](https://forum.arbitrum.foundation/u/lobbyfi)
#### Post date: [May 16, 2025, 9:01am UTC](https://forum.arbitrum.foundation/t/constitutional-aip-arbos-version-40-callisto/28436/46 "2025-05-16T09:01:05Z")
**LobbyFi’s rationale on the price and making the voting power available for sale for this proposal:**
Following the rationale posted [previously](https://forum.arbitrum.foundation/t/constitutional-aip-arbos-version-40-callisto/28436/12), he auction be made available.
The instant buy will be priced at 1% (instead of 0.1%) of our voting power’s worth in ETH terms. This is calculated as 18,422,193 ARB \* 1%, which equals approximately 29.25 ETH.
---
### Author:  [@danielM](https://forum.arbitrum.foundation/u/danielM)
#### Post date: [May 16, 2025, 1:56pm UTC](https://forum.arbitrum.foundation/t/constitutional-aip-arbos-version-40-callisto/28436/47 "2025-05-16T13:56:39Z")
I’m voting yes cause this update helps Arbitrum stay up to date with Ethereum changes, like making wallets more smart. Also it fix small bug and makes things work smoother for devs and users.
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### Author:  [@cp0x](https://forum.arbitrum.foundation/u/cp0x)
#### Post date: [May 16, 2025, 8:26pm UTC](https://forum.arbitrum.foundation/t/constitutional-aip-arbos-version-40-callisto/28436/48 "2025-05-16T20:26:56Z")
I wanted to clarify whether there were any calculations on future profits from commissions?
The thing is that Blobs have changed, so Arbitrum should, in theory, give less to the main Ethereum network for transferring data from Arbitrum.
Will Arbitrum receive more for commissions because of this? If so, how much?
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### Author:  [@paulofonseca](https://forum.arbitrum.foundation/u/paulofonseca)
#### Post date: [May 17, 2025, 9:56am UTC](https://forum.arbitrum.foundation/t/constitutional-aip-arbos-version-40-callisto/28436/49 "2025-05-17T09:56:33Z")
here is the security audit [publications/reviews/2025-04-offchainlabs-arbos40nitro-securityreview.pdf at master · trailofbits/publications · GitHub](https://github.com/trailofbits/publications/blob/master/reviews/2025-04-offchainlabs-arbos40nitro-securityreview.pdf)
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### Author:  [@maxlomu](https://forum.arbitrum.foundation/u/maxlomu)
#### Post date: [May 19, 2025, 3:24pm UTC](https://forum.arbitrum.foundation/t/constitutional-aip-arbos-version-40-callisto/28436/50 "2025-05-19T15:24:56Z")
gm, voted FOR - supporting Pectra and the other updates on Arbitrum.
@Arbitrum would be great if next time you could include a brief summary (on the forum or Tally) outlining how the audit findings - especially high severity ones - have been addressed.
Thanks!
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### Author:  [@Zeptimus](https://forum.arbitrum.foundation/u/Zeptimus)
#### Post date: [May 19, 2025, 9:38pm UTC](https://forum.arbitrum.foundation/t/constitutional-aip-arbos-version-40-callisto/28436/51 "2025-05-19T21:38:33Z")
Voted YES on Tally. I believe staying aligned with Ethereum’s Pectra upgrade is crucial for Arbitrum’s growth.
Petra is running well on mainnet, and I trust the Arbitrum devs to deliver another solid implementation. Let’s do it!
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### Author:  [@Euphoria](https://forum.arbitrum.foundation/u/Euphoria)
#### Post date: [May 20, 2025, 10:30am UTC](https://forum.arbitrum.foundation/t/constitutional-aip-arbos-version-40-callisto/28436/52 "2025-05-20T10:30:21Z")
The following reflects the views of the Lampros DAO governance team, composed of Chain\_L (@Blueweb), @Euphoria, and Hirangi Pandya (@Nyx), based on our combined research, analysis, and ideation.
We are voting FOR this proposal in the Tally voting.
We are in support of the ArbOS 40 Callisto upgrade as it introduces meaningful improvements with the Pectra upgrade. With the security audit concluding positively, we are confident in supporting the proposal during the on-chain vote. This upgrade will also help Arbitrum stay up to date with changes happening on Ethereum.
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### Author:  [@jameskbh](https://forum.arbitrum.foundation/u/jameskbh)
#### Post date: [May 20, 2025, 10:58am UTC](https://forum.arbitrum.foundation/t/constitutional-aip-arbos-version-40-callisto/28436/53 "2025-05-20T10:58:07Z")
I voted FOR. This is an upgrade that brings to Arbitrum several new features and keep the chain in sync with the latest version of ETH Mainnet.
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### Author:  [@danielo](https://forum.arbitrum.foundation/u/danielo)
#### Post date: [May 20, 2025, 3:16pm UTC](https://forum.arbitrum.foundation/t/constitutional-aip-arbos-version-40-callisto/28436/54 "2025-05-20T15:16:54Z")
Voted FOR
the proposal has been well evaluated by technical bodies and is key to keep up with ethereum development
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### Author:  [@paulofonseca](https://forum.arbitrum.foundation/u/paulofonseca)
#### Post date: [May 20, 2025, 4:31pm UTC](https://forum.arbitrum.foundation/t/constitutional-aip-arbos-version-40-callisto/28436/55 "2025-05-20T16:31:21Z")
voting **FOR** on the current onchain vote because this will bring Arbitrum up to par with Ethereum functionality.
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### Author:  [@blockful](https://forum.arbitrum.foundation/u/blockful)
#### Post date: [May 20, 2025, 7:04pm UTC](https://forum.arbitrum.foundation/t/constitutional-aip-arbos-version-40-callisto/28436/56 "2025-05-20T19:04:09Z")
We’ve voted **FOR** this proposal.
Since this AIP ensures Arbitrum stays compatible and aligned with those changes, especially through enhanced Stylus support.
For us, maintaining interoperability with Ethereum and staying in sync with its technical evolution is essential.
We support it as a move that reinforces ecosystem cohesion.
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### Author:  [@Griff](https://forum.arbitrum.foundation/u/Griff)
#### Post date: [May 20, 2025, 9:30pm UTC](https://forum.arbitrum.foundation/t/constitutional-aip-arbos-version-40-callisto/28436/57 "2025-05-20T21:30:10Z")
Voting for, this is one of those “of course we’re doing this” votes. Staying in sync with Ethereum and making things smoother for everyone.
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### Author:  [@KlausBrave](https://forum.arbitrum.foundation/u/KlausBrave)
#### Post date: [May 20, 2025, 11:32pm UTC](https://forum.arbitrum.foundation/t/constitutional-aip-arbos-version-40-callisto/28436/58 "2025-05-20T23:32:31Z")
I voted FOR.
This AIP ensures Arbitrum’s stack is up to date with all the enhancements of Pectra, let’s get this in asap.
Optimism got this done within [48 hours](https://x.com/Optimism/status/1920880156761059545) of ETH’s Petra update, we are still voting on it, in the future I’d like to see more forward planning from @Arbitrum and @offchain to have the audit, and vote lined up earlier in sync with next ETH protocol upgrades. Speed is a competitive advantage, builders wanting to experiment and prototype with new transformative functionality will pick the tech provider who’s live and ready.
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### Author:  [@0xAlex](https://forum.arbitrum.foundation/u/0xAlex)
#### Post date: [May 21, 2025, 9:55am UTC](https://forum.arbitrum.foundation/t/constitutional-aip-arbos-version-40-callisto/28436/59 "2025-05-21T09:55:11Z")
I have voted **FOR** this proposal because it is key to have improvements from Pectra on Arbitrum Chain and I don’t see any points of not doing it.
In my opinion this kind of proposal could be done in an Optimistic way, @Arbitrum and @offchain could proposed it to the DAO with a security report, if after 2 or 3 days no major Delegate put a veto or asked for a vote, it is automatically implemented. This could be a way to gain in efficiency cf @KlausBrave comment and avoid to have all delegates to vote on a proposal that is making consensus.
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### Author:  [@Hawheik](https://forum.arbitrum.foundation/u/Hawheik)
#### Post date: [May 21, 2025, 10:09am UTC](https://forum.arbitrum.foundation/t/constitutional-aip-arbos-version-40-callisto/28436/60 "2025-05-21T10:09:23Z")
I have voted “Yes” to this proposal on Tally. There are significant advantages to staying “in-sync” with Ethereum, and significant disadvantages not to, so it’s a simple decision.
I appreciate @paulofonseca linking the audit reports, and I wish they had been provided more “up-front” rather than relying on a delegate to link them.
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