# EIP-8455 draft clarifies combined gas readings after child calls

Canonical: https://forkbrief.com/news/8ab7cdf0-7f5b-4257-8e71-6367682d6721
Published: 2026-10-28T13:27:21.480Z
Publisher: Fork Brief

An October 28 revision adds guidance and documented cases for refills that move between gas counters. The RESERVOIR proposal remains Draft and unmerged.

An [October 28 revision](https://github.com/ethereum/EIPs/commit/d269755c78f726d8c9ceab5c940d9e8af78e221c) to Ethereum's proposed RESERVOIR opcode clarifies how contracts would measure gas across child calls. The added guidance says to compare the combined `GAS + RESERVOIR` budget before and after a call, because a refill can move between those counters when the child returns.

EIP-8455 proposes exposing state gas that the existing `GAS` reading does not include. Its [pull request](https://github.com/ethereum/EIPs/pull/12577) was opened October 23 and remained open and unmerged when checked October 28. The specification is marked Draft. This revision describes proposed behavior; it does not activate an opcode on Ethereum.

### Why the combined reading matters

Under the draft's reservoir model, state creation draws from a separate reservoir first, then from `gas_left` if that reservoir is exhausted. When a successful child call returns, the merge step can transfer a refill back into `gas_left`.

The [versioned specification](https://github.com/ethereum/EIPs/blob/d269755c78f726d8c9ceab5c940d9e8af78e221c/EIPS/eip-8455.md) adds a concrete two-call example: one child creates a storage slot and another clears it. If the reservoir originally funded the slot, the refill appears in the caller's RESERVOIR reading. If `gas_left` funded it, the caller's GAS reading rises instead, while RESERVOIR can stay unchanged. Looking at only one counter can therefore miss part of the budget change.

The revision also adds corresponding documented cases and an execution-specification test filler. Their presence establishes proposed expectations, rather than an independently reproduced test result.

### Measurement still has boundaries

GAS and RESERVOIR remain separate instructions. Their combined reading is not atomic, and sampling has execution-gas overhead. The draft also covers [EIP-8141 frame transactions](https://forkbrief.com/news/30661c99-d024-47a9-8ed0-b5ac20ffefc4), where RESERVOIR would expose the frame's separate state-gas balance.

A refill can make measured consumption negative. The proposal distinguishes measuring that budget change from deciding how a bundling protocol allocates charges and credits among users. It leaves GAS and the underlying state-accounting rules unchanged.

## Sources

- [EIP-8455: RESERVOIR Opcode (PR \#12577)](https://github.com/ethereum/EIPs/pull/12577) — ethereum/EIPs
- [Clarify GAS + RESERVOIR measurement across child-frame refills](https://github.com/ethereum/EIPs/commit/d269755c78f726d8c9ceab5c940d9e8af78e221c) — ethereum/EIPs
- [EIP-8455 RESERVOIR Opcode: Draft at d269755c78f7](https://github.com/ethereum/EIPs/blob/d269755c78f726d8c9ceab5c940d9e8af78e221c/EIPS/eip-8455.md) — ethereum/EIPs
- [EIP-8455: RESERVOIR Opcode](https://ethereum-magicians.org/t/eip-8455-reservoir-opcode/30116) — Ethereum Magicians

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