Recognition: unknown
From Backward Spreading to Forward Replay: Revisiting Target Construction in LLM Parameter Editing
Pith reviewed 2026-05-09 19:39 UTC · model grok-4.3
The pith
Optimizing the anchor at the first editing layer and propagating forward yields more accurate targets for all layers than backward spreading.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
Instead of optimizing the target hidden-state at the last editing layer and spreading it backward, the method optimizes the anchor at the first editing layer and then propagates it forward, automatically generating accurate and mutually compatible target hidden-states for every subsequent layer at the same computational cost.
What carries the argument
Forward propagation of the anchor point optimized at the first editing layer, which replaces backward spreading from the last layer.
If this is right
- The method achieves identical computational complexity to existing backward-spreading techniques.
- Layer-wise targets are more accurate and mutually compatible across edited layers.
- The approach integrates without changing the initial target computation or any other pipeline components.
- The same forward-propagation construction can be applied to a wide range of existing LLM parameter editing methods.
Where Pith is reading between the lines
- Multi-layer edits may accumulate fewer inconsistencies because targets are generated sequentially from the same starting point rather than adjusted retroactively.
- The change could simplify debugging of editing failures by making the relationship between layers more transparent.
- Similar forward-construction logic might be tested on sequential models outside the LLM setting where hidden-state targets must be defined across layers.
Load-bearing premise
That optimizing the anchor at the first layer and propagating it forward will automatically produce mutually compatible and accurate targets for all later layers without any further adjustments.
What would settle it
An experiment that measures editing success rates or downstream task performance when using forward-propagated targets versus backward-spread targets on the same models and benchmarks, with forward propagation showing clearly worse results.
Figures
read the original abstract
LLM parameter editing methods commonly rely on computing an ideal target hidden-state at a target layer (referred as anchor point) and distributing the target vector to multiple preceding layers (commonly known as backward spreading) for cooperative editing. Although widely used for a long time, its underlying basis have not been systematically investigated. In this paper, we first conduct a systematic study of its foundations, which helps clarify its capability boundaries, practical considerations, and potential failure modes. Then, we propose a simple and elegant alternative that replaces backward spreading with forward-propagation. Instead of optimizing the target at the last editing layer, we optimize the anchor point at the first editing layer, and then propagate it forward to obtain accurate and mutually compatible target hidden-states for all subsequent editing layers. This approach achieves the same computational complexity as existing methods while producing more accurate layer-wise targets. Our method is simple, without interfering with either the computation of the initial target hidden state or any other components of the subsequent editing pipeline, and thus constituting a benefit for a wide range of LLM parameter editing methods.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript first performs a systematic analysis of the foundations, capability boundaries, and failure modes of backward spreading for constructing target hidden states in LLM parameter editing. It then proposes forward replay as an alternative: the anchor hidden state is optimized at the first editing layer so that the original forward pass reaches the desired output, after which the original layer transformations are applied to generate targets for all subsequent editing layers. The authors claim this construction yields more accurate and mutually compatible layer-wise targets at the same computational complexity as backward spreading, without requiring changes to the initial target computation or other pipeline components.
Significance. The systematic study of backward spreading provides a useful clarification of its practical limits. If the forward-replay targets are indeed more accurate and remain compatible under joint multi-layer edits, the method would offer a lightweight, non-disruptive improvement that could be adopted across many existing LLM editing algorithms, potentially raising their reliability on knowledge-editing and model-update benchmarks without added cost.
major comments (2)
- [Abstract] Abstract: the central claim that forward replay 'produces more accurate layer-wise targets' and 'mutually compatible' targets is stated without any quantitative comparison, error analysis, or ablation against backward spreading; the soundness of the improvement therefore rests on an unverified assertion.
- [Method section] Method section (forward-replay construction): the proposal optimizes the anchor at the first editing layer and propagates using the original inter-layer maps. When multiple layers are edited simultaneously, however, the edited model's hidden-state trajectory deviates from the original trajectory, so the pre-computed forward targets are no longer guaranteed to be the fixed points required by the joint editing objective. No analysis, proof, or counter-example addressing this compatibility risk is supplied.
Simulated Author's Rebuttal
We thank the referee for the constructive review and recommendation for major revision. We address each major comment below, agreeing that the claims require stronger quantitative support and explicit analysis of multi-layer compatibility. We will incorporate the necessary additions in the revised manuscript.
read point-by-point responses
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Referee: [Abstract] Abstract: the central claim that forward replay 'produces more accurate layer-wise targets' and 'mutually compatible' targets is stated without any quantitative comparison, error analysis, or ablation against backward spreading; the soundness of the improvement therefore rests on an unverified assertion.
Authors: We agree that the abstract presents the accuracy and compatibility claims without direct quantitative backing. The manuscript's core contribution is the systematic analysis of backward spreading's foundations, boundaries, and failure modes, which motivates forward replay as an alternative that avoids those issues by construction. To address the concern, we will revise the abstract for precision and add quantitative comparisons (e.g., layer-wise reconstruction error relative to the original forward pass) plus ablation studies on editing benchmarks in a new results subsection. These will directly validate the claims against backward spreading at equivalent cost. revision: yes
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Referee: [Method section] Method section (forward-replay construction): the proposal optimizes the anchor at the first editing layer and propagates using the original inter-layer maps. When multiple layers are edited simultaneously, however, the edited model's hidden-state trajectory deviates from the original trajectory, so the pre-computed forward targets are no longer guaranteed to be the fixed points required by the joint editing objective. No analysis, proof, or counter-example addressing this compatibility risk is supplied.
Authors: This highlights a valid subtlety in joint multi-layer editing. Forward replay constructs targets by optimizing the anchor at the first layer and propagating via the original transformations, ensuring consistency with the unmodified forward trajectory from that anchor. While simultaneous edits will alter the actual trajectory, the targets remain mutually compatible as they derive from a single optimized starting point rather than independent backward computations. We will expand the method section with a dedicated discussion of this approximation, including conditions for validity and empirical counter-examples on multi-layer edits, to clarify the risk without altering the core algorithm. revision: yes
Circularity Check
No circularity: forward-propagation proposal is an independent construction
full rationale
The paper first analyzes the foundations and failure modes of backward spreading, then introduces forward replay as a direct alternative: optimize the anchor hidden state at the earliest editing layer and propagate it forward using the original layer transformations to obtain targets for later layers. This is explicitly framed as a simple substitution that preserves computational complexity, does not alter the initial target computation or other pipeline components, and yields 'more accurate and mutually compatible' targets by construction of the forward pass. No equations reduce the claimed accuracy or compatibility to a fitted parameter drawn from the same data used for evaluation, nor does any step rename a known result or import a uniqueness theorem via self-citation. The central modeling choice (that original inter-layer maps remain useful for target construction) is a substantive assumption open to empirical test rather than a self-definitional loop. The derivation chain is therefore self-contained against external benchmarks.
Axiom & Free-Parameter Ledger
axioms (1)
- domain assumption Forward propagation from an optimized anchor at the first editing layer produces mutually compatible and more accurate targets for subsequent layers.
Reference graph
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discussion (0)
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