update: merge arbos51 upgrade notices

Author: zk-Lumi

docs/notices/arbos51-arbmainnet-upgrade-notice.mdx

@@ -1,23 +1,34 @@
 ---
-title: 'ArbOS 51 activation on ArbSepolia'
-description: Upgrade notices for ArbOS 51 activation on ArbSepolia
-user_story: As an Arbitrum chain owner or node operator, I want to configure my chain/nodes to run on ArbSepolia.
+title: 'Upgrade notice for ArbOS 51'
+description: Upgrade notices for ArbOS 51 activation on Arbitrum One, Arbitrum Nova, and Arbitrum Spolia
+user_story: As an Arbitrum node operator, I want to keep my nodes in sync with Arbitrum One, Arbitrum Nova, and Arbitrum Sepolia after the ArbOS 51 activation.
 content_type: notice
 ---
 
-On Monday, December 1, 2025 at 17:00 UTC, [ArbOS 51 "Dia"](docs/run-arbitrum-node/arbos-releases/arbos51.mdx) will activate on the Arbitrum Sepolia chain.
+[ArbOS 51 "Dia"](docs/run-arbitrum-node/arbos-releases/arbos51.mdx) will be activated on the Arbitrum Sepolia, Arbitrum One, and Arbitrum Nova chains.
+
+## Actions required for node operators
 
 :::warning Action required
 
-Arbitrum Sepolia node operators **must upgrade** to Nitro **`v3.9.3`** ahead of this activation to continue syncing the chain.
+Arbitrum node operators **must upgrade** to Nitro **`v3.9.3`** ahead of ArbOS 51 activation to continue syncing the chain.
 
 - **Docker image:** `offchainlabs/nitro-node:v3.9.3-8bc5554`
 - **Release notes:** https://github.com/OffchainLabs/nitro/releases/tag/v3.9.3
 
 :::
 
-### Context
+## Important dates
+
+The following dates are relevant for Arbitrum chain operators.
+
+| Date                          | Network upgrade                       | Affected audience                    |
+| ----------------------------- | ------------------------------------- | ------------------------------------ |
+| `Dec 1st 2025, 17:00:00 UTC`  | Arbitrum Sepolia upgrade to ArbOS 51  | Node operators for Arbitrum Sepolia  |
+| `Jan 8th, 2026, 17:00:00 UTC` | Arbitrum One/Nova upgrade to ArbOS 51 | Node operators for Arbitrum One/Nova |
+
+## Context
 
-[ArbOS 51](docs/run-arbitrum-node/arbos-releases/arbos51.mdx) is a follow-up to ArbOS 50 that fixes issues with the pricing framework. ArbOS 50 was previously activated on Sepolia, but the Gas Target & Pricing Framework changes remained disabled pending this fix. ArbOS 51 now completes that work.
+[ArbOS 51 "Dia"](docs/run-arbitrum-node/arbos-releases/arbos51.mdx) builds upon [ArbOS 40 "Callisto"](docs/run-arbitrum-node/arbos-releases/arbos40.mdx) with support for the relevant EVM changes that are a part of Ethereum's [Fusaka upgrade](https://ethereum.org/en/roadmap/fusaka/), as well as additional improvements to the gas pricing algorithm, a change to the min L2 base fee, `MaxTxGasLimit` allowing full block utilization, changes to instrument Nitro’s State Transition Function (STF) to price gas based on specific resource usage, native token mint/burn capabilities, and a few bug fixes.
 
-Upstream governance items ([ArbOS 50](https://snapshot.box/#/s:arbitrumfoundation.eth/proposal/0x33754da4006d0ef38666ec5d5e85fd0966a891a594ab9dc21f23beedea2d330b) + [Gas Target & Pricing Framework](https://snapshot.box/#/s:arbitrumfoundation.eth/proposal/0x4a96a91d162975de0d402b83ca8b8a24e808ca357150120fc0d44ae0bf1cc4a5)) are being bundled into a single on-chain vote. Both components have passed Snapshot temperature checks, with the Tally vote expected to open on or around **December 4, 2025**.
+Upstream governance items ([ArbOS 50](https://snapshot.box/#/s:arbitrumfoundation.eth/proposal/0x33754da4006d0ef38666ec5d5e85fd0966a891a594ab9dc21f23beedea2d330b) + [Gas Target & Pricing Framework](https://snapshot.box/#/s:arbitrumfoundation.eth/proposal/0x4a96a91d162975de0d402b83ca8b8a24e808ca357150120fc0d44ae0bf1cc4a5)) were bundled into a single [ArbOS 51 on-chain vote](https://www.tally.xyz/gov/arbitrum/proposal/53154361738756237993090798888616593723057470462495169047773178676976253908001?govId=eip155:42161:0xf07DeD9dC292157749B6Fd268E37DF6EA38395B9). Both components have passed Snapshot temperature checks, and the bundled Tally vote was passed **December 18, 2025**.

docs/notices/arbos51-arbsepolia-upgrade-notice.mdx

@@ -97,7 +97,7 @@ const sidebars = {
     {
       type: 'link',
       label: 'Notices',
-      href: '/notices/arbos51-arbmainnet-upgrade-notice',
+      href: '/notices/arbos51-arbsepolia-upgrade-notice',
     },
     {
       type: 'doc',
@@ -1526,15 +1526,10 @@ const sidebars = {
 
   // Notices sidebar
   noticeSidebar: [
-    {
-      type: 'doc',
-      id: 'notices/arbos51-arbmainnet-upgrade-notice',
-      label: 'Upgrade for ArbOS 51 on Arbitrum One & Nova',
-    },
     {
       type: 'doc',
       id: 'notices/arbos51-arbsepolia-upgrade-notice',
-      label: 'Upgrade for ArbOS 51 on ArbSepolia',
+      label: 'Upgrade notice for ArbOS 51',
     },
     {
       type: 'doc',

sidebars.js

@@ -1488,12 +1488,12 @@
     },
     {
       "source": "/(notices/arbos-50/?)",
-      "destination": "/notices/arbos51-arbmainnet-upgrade-notice",
+      "destination": "/notices/arbos51-arbsepolia-upgrade-notice",
       "permanent": false
     },
     {
       "source": "/(notices/arbos-51/?)",
-      "destination": "/notices/arbos51-arbmainnet-upgrade-notice",
+      "destination": "/notices/arbos51-arbsepolia-upgrade-notice",
       "permanent": false
     },
     {