docs: README uses non-copyable `0x000....64` shorthand for the ArbSys precompile address

[mssystem1]

Summary

The Nitro README documents the ArbSys precompile using the shorthand address:

0x000....64

This is not a syntactically valid Ethereum address.

Because this section explicitly tells users that they can call arbOSVersion() on the precompile to verify the currently active ArbOS version, using a non-copyable address makes the operational example unnecessarily difficult to use.

Affected File

Repository:

OffchainLabs/nitro

File:

README.md

Section:

Special note about ArbOS & Arbitrum Classic

Current Documentation

The README says that the ArbOS version can be verified using:

arbOSVersion()

on:

0x000....64

Problem

Ethereum tooling expects a complete 20-byte address.

For example, this cannot be passed directly to:

cast call 0x000....64 ...

or to:

viem.readContract(...)

because:

0x000....64

is not valid hexadecimal and is not a valid Ethereum address.

Users therefore have to already know the real ArbSys address before they can follow the verification instructions.

Expected Behavior

Documentation describing a callable contract/precompile should use the full canonical address.

For example:

0x0000000000000000000000000000000000000064

if that is the intended ArbSys address.

Suggested Fix

Replace the shorthand notation with the complete address.

For example:

- ArbSys precompile at `0x000....64`
+ ArbSys precompile at `0x0000000000000000000000000000000000000064`

Additional Improvement

Since the section is specifically about verifying ArbOS versions, consider adding a directly executable example.

For example:

cast call \
  0x0000000000000000000000000000000000000064 \
  "arbOSVersion()(uint256)" \
  --rpc-url <ARBITRUM_RPC_URL>

Then explain the version mapping immediately below it.

Why This Matters

The current section is operational documentation.

A user reading it is likely trying to verify:

• the active ArbOS version;
• whether an upgrade has activated;
• whether their node/network is on the expected version.

Providing a complete address removes ambiguity and makes the check directly reproducible.

Impact

Severity: Low

Category:

• documentation;
• operator experience;
• developer experience.

No runtime behavior is affected.

Steps to Reproduce

1. Open the Nitro README.
2. Navigate to Special note about ArbOS & Arbitrum Classic.
3. Copy:

0x000....64

4. Pass it to an Ethereum CLI or JavaScript address parser.
5. Observe that it is rejected as an invalid address.

Environment

Repository:

OffchainLabs/nitro

Branch:

master

Affected file:

README.md