> ## Documentation Index
> Fetch the complete documentation index at: https://docs.biconomy.io/llms.txt
> Use this file to discover all available pages before exploring further.

# MEE Versions

The **Modular Execution Environment (MEE)** supports multiple versions of its contract suite. Each version introduces new capabilities around **smart accounts**, **validator configuration**, and **composability**.

<Info>
  This guide helps SDK developers understand and select the appropriate version for their use case.
</Info>

## Versions Table

The table below outlines all supported MEE versions and their core capabilities. Use this to determine the best version for your project based on EVM support, composability, and ERC-7702 compatibility.

| Version | Nexus Version | ERC-7702 Support | Composability | Notes                                                                                                                                             |
| ------- | ------------- | ---------------- | ------------- | ------------------------------------------------------------------------------------------------------------------------------------------------- |
| `2.3.0` | 1.3.1         | ✅ Yes            | ✅️ Native     | **Experimental and unaudited** Adds new `safe-sa` fusion mode that enables Safw accounts with multichain orchestration features                   |
| `2.2.2` | 1.3.2         | ✅ Yes            | ✅️ Native     | Bundles the audited [ERC-8211 Smart Batching](https://www.erc8211.com) reference implementation (EF & Biconomy). Audited by Pashov (May 2026).    |
| `2.2.1` | 1.3.1         | ✅ Yes            | ✅️ Native     | **Latest** Adds new [composability features](/new/getting-started/understanding-runtime-injection) and EIP-712 typed data sign for some stx modes |
| `2.1.0` | 1.2.0         | ✅ Yes            | ✅ Native      | **SDK default** Allows delegated/upgraded EOAs to directly own smart accounts in Nexus 1.2.0.                                                     |
| `2.0.0` | 1.2.0         | ✅ Yes            | ✅ Native      | Supports ERC-7702 flows but **does not** support delegated/upgraded EOAs as direct owners of smart accounts.                                      |
| `1.1.0` | 1.0.2         | ❌ No             | ⚠️ Manual     | Composability must be installed manually (handled by the SDK). Best for EVM Paris–only chains with limited opcode support.                        |
| `1.0.0` | 1.0.2         | ❌ No             | ⚠️ Manual     | Same as `1.1.0`. Composability module installed via SDK.                                                                                          |

## Version Breakdown

<Tabs>
  <Tab title="v2.3.0 (Experimental)">
    <div className="flex items-start space-x-3 mb-4">
      <div className="flex-shrink-0">
        <div className="w-8 h-8 bg-orange-100 rounded-full flex items-center justify-center">
          <span className="text-orange-600 font-semibold text-sm">!!</span>
        </div>
      </div>

      <div>
        <h4 className="text-lg font-semibold text-green-600 mb-2">Experimental and unaudited</h4>
        <p className="text-gray-600 mb-3">Unlocks cross-chain orchestration for Safe accounts</p>
      </div>
    </div>

    **Key Features:**

    * Safe accounts can now be used as master accounts in Fusion flow as well as EOAs.
      * Flow is the same as for EOA's, just instead of one master EOA signature, the proper multisig is required to initiate a SuperTxn
      * Safe accounts should be deployed at the same address on all the chains involved in the SuperTxn (source and destination chains)

    <Tip>
      **Recommended for projects on early stages** looking to attract the large Safe multisig accounts userbase.
    </Tip>
  </Tab>

  <Tab title="v2.2.2">
    <div className="flex items-start space-x-3 mb-4">
      <div className="flex-shrink-0">
        <div className="w-8 h-8 bg-green-100 rounded-full flex items-center justify-center">
          <span className="text-green-600 font-semibold text-sm">★</span>
        </div>
      </div>

      <div>
        <h4 className="text-lg font-semibold text-green-600 mb-2">Audited ERC-8211 reference implementation</h4>
        <p className="text-gray-600 mb-3">Nexus 1.3.2 bundling the audited [ERC-8211 Smart Batching](https://www.erc8211.com) reference implementation</p>
      </div>
    </div>

    **Key Features:**

    * Bundles the audited [ERC-8211 Smart Batching](https://www.erc8211.com) reference implementation (Ethereum Foundation & Biconomy) — the formal standardization of the composability primitives shipped in earlier versions
    * Expanded composability primitives and pipeline hardening
    * Audited by Pashov (May 2026)

    <Tip>
      **Opt-in upgrade.** Will become the default once the STX API supports it natively.
    </Tip>
  </Tab>

  <Tab title="v2.2.1 (Latest)">
    <div className="flex items-start space-x-3 mb-4">
      <div className="flex-shrink-0">
        <div className="w-8 h-8 bg-green-100 rounded-full flex items-center justify-center">
          <span className="text-green-600 font-semibold text-sm">★</span>
        </div>
      </div>

      <div>
        <h4 className="text-lg font-semibold text-green-600 mb-2">Reachest features prior to v2.2.2</h4>
        <p className="text-gray-600 mb-3">Built on Nexus 1.3.1 with extended composability features</p>
      </div>
    </div>

    **Key Features:**

    * Adds native token runtime injection feature
    * Adds runtime injection via custom static call (inject ANY return value as an input param at the runtime)
    * Users signs EIP-712 Data Struct instead of blind Stx hash for the `smart-account` mode
    * Allows initializing new Nexus ERC-7702 account via relayer with an owner issued signature (gasless ERC-7702 delegation)

    <Tip>
      **Recommended for projects** seeking the latest features for the [runtime injection](new/getting-started/understanding-runtime-injection) and wanting to provide transparent EIP-712 sig requests for users.
    </Tip>
  </Tab>

  <Tab title="v2.1.0 (Default)">
    <div className="flex items-start space-x-3 mb-4">
      <div className="flex-shrink-0">
        <div className="w-8 h-8 bg-green-100 rounded-full flex items-center justify-center">
          <span className="text-green-600 font-semibold text-sm">★</span>
        </div>
      </div>

      <div>
        <h4 className="text-lg font-semibold text-green-600 mb-2">SDK default</h4>
        <p className="text-gray-600 mb-3">Built on Nexus 1.2.0 with cutting-edge capabilities</p>
      </div>
    </div>

    **Key Features:**

    * Fully supports **ERC-7702**, including **delegated/upgraded EOAs** as direct owners of Smart Contract Accounts (SCAs)
    * Features **native composability** — no need for manual module installation
    * Built on Nexus `1.2.0` with pre-installed MEE K1 validator

    <Tip>
      **Recommended for all new projects** seeking the simplest and most battle-tested developer experience.
    </Tip>
  </Tab>

  <Tab title="v2.0.0">
    <div className="flex items-start space-x-3 mb-4">
      <div className="flex-shrink-0">
        <div className="w-8 h-8 bg-blue-100 rounded-full flex items-center justify-center">
          <span className="text-blue-600 font-semibold text-sm">2.0</span>
        </div>
      </div>

      <div>
        <h4 className="text-lg font-semibold text-blue-600 mb-2">Native Composability, No Delegated EOAs</h4>
        <p className="text-gray-600 mb-3">ERC-7702 support with composability built-in</p>
      </div>
    </div>

    **Key Features:**

    * Supports **ERC-7702**, but **does not allow delegated or upgraded EOAs** to directly own smart accounts
    * Includes **native composability**, reducing setup complexity

    <Note>
      Suitable for applications that do not require EOAs as direct smart account owners but want full ERC-7702 support.
    </Note>
  </Tab>

  <Tab title="v1.1.0">
    <div className="flex items-start space-x-3 mb-4">
      <div className="flex-shrink-0">
        <div className="w-8 h-8 bg-orange-100 rounded-full flex items-center justify-center">
          <span className="text-orange-600 font-semibold text-sm">1.1</span>
        </div>
      </div>

      <div>
        <h4 className="text-lg font-semibold text-orange-600 mb-2">EVM Paris Compatibility with Manual Composability</h4>
        <p className="text-gray-600 mb-3">For chains limited to Paris upgrade opcodes</p>
      </div>
    </div>

    **Key Features:**

    * Does **not support ERC-7702**
    * Requires **manual installation** of composability modules, though the SDK automates this during deployment

    <Note>
      Targeted for EVM chains limited to Paris upgrade opcodes (no PUSH0, MCOPY, or TSTORE). Good choice for compatibility-constrained environments.
    </Note>
  </Tab>

  <Tab title="v1.0.0">
    <div className="flex items-start space-x-3 mb-4">
      <div className="flex-shrink-0">
        <div className="w-8 h-8 bg-gray-100 rounded-full flex items-center justify-center">
          <span className="text-gray-600 font-semibold text-sm">1.0</span>
        </div>
      </div>

      <div>
        <h4 className="text-lg font-semibold text-gray-600 mb-2">Supports all EVM chains prior to the Cancun upgrade</h4>
        <p className="text-gray-600 mb-3">Legacy compatibility for older EVM environments</p>
      </div>
    </div>

    **Key Features:**

    * No ERC-7702 support
    * Requires manual installation of composability modules, automatically handled by the SDK
    * Compatible with all EVM environments **below the Cancun upgrade**

    <Note>
      Suitable for legacy or specialized chains where native composability isn't available but can be enabled via modules.
    </Note>
  </Tab>
</Tabs>

## Recommendation

For most development needs, **version >= `2.1.0` is strongly recommended** due to its full support for delegated EOAs and native composability.
Version `2.2.1` is currently the SDK/STX default. Version `2.2.2` is available as an opt-in upgrade that bundles the audited [ERC-8211 Smart Batching](https://www.erc8211.com) reference implementation, and will become the default once the STX API supports it natively.
Earlier versions remain available for legacy or specialized chains but require additional setup steps handled by the SDK.

<CodeGroup>
  ```typescript Example usage in SDK theme={null}
  import { MEEVersion } from "@your-sdk/core";

  const version = MEEVersion.V2_1_0;
  ```
</CodeGroup>

## How to Find Your Current Nexus Version

Not sure which Nexus version your smart account is using? Follow these simple steps to find out:

<Steps>
  <Step title="Locate your smart account address">
    **Locate your existing Nexus smart account address** on the specific blockchain you're working with.
  </Step>

  <Step title="Open the block explorer">
    **Open the block explorer** for that chain (e.g., Etherscan, Polygonscan) and paste the smart account address into the search bar.
  </Step>

  <Step title="Navigate to the Contracts tab">
    Navigate to the **Contracts** tab on the explorer page.
  </Step>

  <Step title="Verify the proxy contract if needed">
    If the contract is a **proxy** and the proxy contract isn't verified yet, you'll need to verify it first. (If "Read as proxy" option isn't available, this usually means verification is needed.)
  </Step>

  <Step title="Call the getImplementation function">
    Once verified, go to the **Read as proxy** section and call the `getImplementation` function. This will return the address of the actual implementation contract your smart account is using.
  </Step>

  <Step title="Compare with official addresses">
    Compare this implementation contract address against the addresses listed on our [Contracts and Audits](/contracts-and-audits) page. This will help you identify exactly which MEE version you are using.
  </Step>
</Steps>

If you need further assistance, feel free to join our [Discord community](https://discord.gg/biconomy) and ask for help!

<Tip>
  Keeping track of your Nexus version is key for smooth upgrades and compatibility checks.
</Tip>

## Not Sure Which Version to Choose?

If you're still confused about which MEE version fits your needs, or if you're unsure about your current version for migration, don't worry!

Join our [Discord community](https://discord.gg/biconomy) to ask questions and get real-time support from the team and other developers.

We're here to help you choose the best path forward!