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

# Osaka on L2

> Learn about the Osaka EIP activations on L2, including the EIP-7825 per-transaction gas limit and precompile gas changes.

<Info>
  This feature ships with [Upgrade 19](/notices/upgrade-19). It is non-functional until the upgrade is approved by governance and activated on Mainnet.
</Info>

Upgrade 19 activates a subset of the Osaka EIPs on L2 — specifically the changes that are applicable to OP Stack chains. Not every Osaka EIP is relevant to L2 execution; only those that affect L2 transaction processing or precompile behavior are included.

The activated changes introduce a per-transaction gas limit and updated gas costs for two precompiles.

## EIP-7825: Per-transaction gas limit

[EIP-7825](https://eips.ethereum.org/EIPS/eip-7825) introduces a maximum gas limit that any single L2 transaction can request. After Upgrade 19, transactions whose gas limit exceeds this threshold are rejected as invalid by the execution layer.

The EIP-7825 limit is 2^24 = **16,777,216 gas**.
It is enforced by the execution client (`op-reth`).

### Deposit transactions are exempt

Deposit transactions (L1-to-L2 messages) are **not** subject to the EIP-7825 limit. Deposits are already capped at 20M gas total per L1 block, and rejecting a deposit on L2 that was accepted on L1 would cause permanent ETH loss. System deposit transactions (e.g., network upgrade transactions) are also exempt.

### Impact on app developers

Most transactions will not be affected. The limit is designed to be well above gas requirements for typical application interactions. If your application submits transactions with very high gas limits, verify they remain within the new threshold.

If your application constructs raw transactions programmatically and sets a gas limit above the threshold, those transactions will fail. Update your gas limit logic or rely on standard `eth_estimateGas` responses — estimates will not return a value above the limit.

## MODEXP gas cost and input size changes

[EIP-7883](https://eips.ethereum.org/EIPS/eip-7883) raises the `MODEXP` precompile (`0x05`) gas cost floor from 200 to 500 gas.
[EIP-7823](https://eips.ethereum.org/EIPS/eip-7823) caps the modulus size at 1024 bytes — calls with a larger declared modulus fail.

* **For contracts using `MODEXP`:** re-run gas benchmarks and update any hardcoded gas values. Verify that your modulus inputs are within the 1024-byte limit.
* **For contracts not using `MODEXP`:** no action required.

## P256VERIFY gas cost change

[EIP-7951](https://eips.ethereum.org/EIPS/eip-7951) raises the `P256VERIFY` precompile (`0x100`) gas cost from 3,450 (RIP-7212) to **6,900 gas**.

* **For contracts using `P256VERIFY`:** re-run gas benchmarks and update any hardcoded gas values.
* **For contracts not using `P256VERIFY`:** no action required.

## CLZ opcode

[EIP-7939](https://eips.ethereum.org/EIPS/eip-7939) introduces the Count Leading Zeros opcode (`CLZ`, `0x1e`).
Given a `uint256`, it returns the number of leading zero bits (0–255).

* **For contract developers:** the opcode is now available for use. Existing contracts are not affected.
* **For toolchain authors:** assemblers and decompilers that treat unknown opcodes as invalid should add `CLZ` support.

## Summary of changes

| Change                                             | EIP                                                 | OPCODE        | Impact                                                     |
| -------------------------------------------------- | --------------------------------------------------- | ------------- | ---------------------------------------------------------- |
| Per-transaction gas limit (16,777,216 gas)         | [EIP-7825](https://eips.ethereum.org/EIPS/eip-7825) | n/a           | Transactions above the limit are invalid (deposits exempt) |
| `MODEXP` gas floor increase (200 → 500 gas)        | [EIP-7883](https://eips.ethereum.org/EIPS/eip-7883) | `0x05`        | Gas cost changes                                           |
| `MODEXP` modulus size cap (1024 bytes)             | [EIP-7823](https://eips.ethereum.org/EIPS/eip-7823) | `0x05`        | Inputs over 1024-byte modulus fail                         |
| `P256VERIFY` gas cost increase (3,450 → 6,900 gas) | [EIP-7951](https://eips.ethereum.org/EIPS/eip-7951) | `0x100`       | Gas cost changes                                           |
| CLZ (Count Leading Zeros) opcode                   | [EIP-7939](https://eips.ethereum.org/EIPS/eip-7939) | opcode `0x1e` | New opcode available                                       |

## References

* [Karst spec overview](https://specs.optimism.io/protocol/karst/overview.html)
* [Karst exec-engine spec](https://specs.optimism.io/protocol/karst/exec-engine.html)
* [Osaka on L2 design document](https://github.com/ethereum-optimism/design-docs/blob/main/protocol/osaka-on-l2.md)
* [EIP-7825](https://eips.ethereum.org/EIPS/eip-7825)
* [EIP-7883](https://eips.ethereum.org/EIPS/eip-7883)
* [EIP-7823](https://eips.ethereum.org/EIPS/eip-7823)
* [EIP-7951](https://eips.ethereum.org/EIPS/eip-7951)
* [EIP-7939](https://eips.ethereum.org/EIPS/eip-7939)
* [Upgrade 19 notice](/notices/upgrade-19)