> ## Documentation Index
> Fetch the complete documentation index at: https://base-a060aa97-roethke-b20-upgrade-pages.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Overview

> Cobalt improves the B20 token standard, adds validity transactions, introduces dynamic node upgrades, and migrates TEE signer registration to onchain attestation verification.

| | Status | Date |
| - | - | - |
| Sepolia | Live | September 23, 2026 |
| Mainnet | Shipping | September 30, 2026 |

## Features

<AccordionGroup>
  <Accordion title="B20 Improvements">
    **Base** · Precompile

    Cobalt brings improvements to the B20 token standard: pay transaction fees in B20s, schedule multiplier updates, transfer blocked simplification, and new Union and Intersect policies.
  </Accordion>

  <Accordion title="Validity Transactions">
    **Base** · Transactions

    Cobalt introduces validity transactions: signed transactions that Base includes only when onchain conditions (balance, storage, block-number, and Flashblock-index predicates) match. Use them for conditional swaps, withdrawals, and other state-dependent actions. See [Validity Transactions](/specifications/build-transaction/validity-transactions) for the full specification.
  </Accordion>

  <Accordion title="Dynamic Upgrades">
    **Base** · RPC

    Dynamic Upgrades introduces an Ethereum smart contract that stores upgrade timestamps for Base nodes, allowing nodes to query the contract and apply changes live. This change will be rolled out in metrics-only mode on Mainnet as data is collected to validate that the upgrades work smoothly.
  </Accordion>

  <Accordion title="TEE Registration Migration">
    **Base** · Infrastructure

    Cobalt changes how new Trusted Execution Environment (TEE) signers are registered: AWS Nitro attestations are trustlessly verified fully onchain using checked P-384 hints, replacing the RISC Zero and Boundless proving flow. Registration is faster and no longer depends on an external offchain proving service. Enclave key generation, PCR0 image selection, and proof verification are unchanged. See [Registrar](/specifications/base-protocol/proofs/registrar) for the full specification.
  </Accordion>
</AccordionGroup>