Base Sets Sept. 30 Date for Cobalt Mainnet Upgrade

The deployment represents another infrastructure milestone for Base as the Ethereum Layer 2 expands its focus across global markets, payments, stablecoins and developer applications.

Cobalt Moves From Sepolia to Mainnet

Base completed the Cobalt upgrade on Sepolia on September 23.

The testnet deployment began at 18:00 UTC and was marked complete at 20:00 UTC, according to Base's status page.

With that stage completed, attention now shifts to mainnet.

The current schedule is:

September 23: Base Sepolia Cobalt upgrade completed

September 30 at 18:00 UTC: Base Mainnet Cobalt activation begins

September 30 at 20:00 UTC: Scheduled maintenance window ends

Base says mainnet node operators must be running v1.4.2 or greater.

What Node Operators Need to Do

The most immediate impact of Cobalt is on infrastructure providers operating Base nodes.

Operators need to update their Base software before the mainnet activation to remain compatible with the network after the upgrade.

Base has also moved its public node software to the unified base/base GitHub repository, replacing the previous base/node location.

For regular Base users, the upgrade should happen at the protocol level rather than requiring manual migration of assets.

Users should not need to move ETH or other Base assets simply because Cobalt is being activated.

Cobalt Arrives as Base Expands Its Infrastructure

The upgrade comes during a broader infrastructure push at Base.

Base's 2026 strategy focuses on three major areas:

• Building global markets

• Scaling payments and stablecoins

• Expanding its builder ecosystem

Base says it processed more than $17 trillion in stablecoin volume during 2025, covering 26 local currencies across 17 countries.

The network is also working on chain-level infrastructure for markets, new standards for smart accounts and tokens, and scaling improvements aimed at maintaining fast and inexpensive settlement.

Base Launches 100 ETH Global Buildathons

The Cobalt deployment is happening just as Base begins another major developer initiative.

Base Around the World will run regional buildathons across:

• Africa

• India

• Southeast Asia

• Latin America

The buildathons begin September 27, with the main regional programs running through October 13.

Base is offering a combined 100 ETH prize pool, with 25 ETH allocated to each region.

Developers are being encouraged to build applications addressing local problems, including ecommerce, social applications, creator tools, education and access to onchain financial infrastructure.

Tokenized Stocks Expand Base's Financial Ecosystem

Base is also expanding into tokenized traditional assets.

Coinbase-issued tokenized stocks are now live natively on Base for eligible users outside the United States.

Base says the assets are built using the B20 standard and represent shares held 1:1 by a regulated custodian.

That gives developers the ability to integrate tokenized equities into DeFi and other onchain applications.

Potential applications include:

Onchain brokerages

Portfolio management

Stock-backed lending

Automated trading strategies

Derivatives

AI-managed portfolios

Prediction markets

Base says tokenized equities can interact with wallets, decentralized exchanges and other protocols across its ecosystem.

Availability remains subject to eligibility and jurisdictional restrictions.

Why Infrastructure Upgrades Matter

Base's expansion into payments, tokenized assets and global financial applications increases the importance of reliable underlying infrastructure.

The network is already positioning itself as more than a conventional DeFi chain.

Its 2026 strategy includes stablecoin payments, global markets, tokenized assets and applications used by both people and AI agents.

Infrastructure upgrades such as Cobalt therefore form part of a larger effort to prepare Base for more complex and higher-volume applications.

Base ultimately settles transactions on Ethereum while using the OP Stack to provide faster and lower-cost execution.

What Happens Next?

The immediate milestone is the September 30 mainnet activation.

Node operators will need to ensure they are running v1.4.2 or later before the upgrade.

The Sepolia deployment has already provided a test environment for Cobalt, but mainnet activation will be the more significant milestone for applications and infrastructure providers.

Developers and operators will be watching the network closely during and after the scheduled maintenance window for any compatibility or performance issues.

Meanwhile, Base's broader ecosystem expansion continues through its global buildathons and tokenized-asset initiatives.

Bottom Line

Base will activate its Cobalt mainnet upgrade on September 30, one week after completing the Sepolia deployment.

The scheduled mainnet maintenance window runs from 18:00 to 20:00 UTC, and Base node operators must upgrade to software version 1.4.2 or later.

The upgrade arrives during a broader period of expansion for Base.

The network is simultaneously pushing into global payments, stablecoins, tokenized stocks and developer programs, including its 100 ETH Base Around the World buildathons.

With Sepolia testing complete, September 30 is now the key infrastructure date to watch as Cobalt moves onto Base mainnet.

Base — Official Network Status

Base — Cobalt v1.4.2

Base — 2026 Mission, Vision and Strategy

Base — Base Around the World

Base — Tokenized Stocks