AgentDevel: Regression-Aware LLM Pipeline

• AgentDevel is a framework for LLM agent development that uses flip-centered gating to monitor per-example regressions and fixes.
• It formalizes iterative improvements by tracking pass-to-fail (P→F) and fail-to-pass (F→P) flips for precise, auditable quality control.
• Empirical evaluations demonstrate that AgentDevel maintains low regression rates and minimizes undesirable releases compared to traditional approaches.

AgentDevel is a release engineering framework for LLM agents, formalizing iterative agent improvement as a regression-aware pipeline centered on per-example behavioral flips. It introduces the flip-centered gating paradigm, prioritizing the explicit tracking and gating of pass-to-fail (P→F) regressions and fail-to-pass (F→P) fixes over aggregate metrics, thereby maximizing auditability, reproducibility, and non-regression guarantees during LLM agent development and automated repair (Zhang, 8 Jan 2026).

1. Conceptual Foundations and Formalism

AgentDevel refines agent self-evolution into a disciplined, software engineering-guided loop, replacing unconstrained self-improvement or population search with a single canonical version line. At each iteration $t$, the current blueprint $b_t$ generates a release candidate $b_t^{\rm RC}$. For every training example $x \in D_{\rm train}$, pass indicators are defined by $p_t(x) \in \{0,1\}$ for $b_t$ and $p_t^{\rm RC}(x)$ for $b_t^{\rm RC}$. The “flip sets” are then:

$$\begin{aligned} \mathrm{P2F}_t &= \{\,x \mid p_t(x)=1,\,p_t^{\rm RC}(x)=0\}, \ \mathrm{F2P}_t &= \{\,x \mid p_t(x)=0,\,p_t^{\rm RC}(x)=1\}. \end{aligned}$$

Release promotion is decided by a gate function $G$ as follows:

$$\mathrm{Accept}_t = G(\mathcal{R}_t,\;\mathcal{R}_t^{\rm RC},\;\mathrm{P2F}_t,\;\mathrm{F2P}_t,\;\mathcal{I}_t) \in \{0,1\}$$

where $\mathcal{R}_t, \mathcal{R}_t^{\rm RC}$ are detailed per-example run records, and $\mathcal{I}_t$ is the intended change description. The RC is promoted ($\mathrm{Accept}_t = 1$) only if regression risk (size of $\mathrm{P2F}_t$) remains below a threshold, sufficient F→P fixes are delivered, and those fixes align with $\mathcal{I}_t$.

2. Motivation: Regression-Aware, Audit-First Gating

AgentDevel is motivated by principles from industrial Continuous Integration, where singular new failures block releases regardless of aggregate improvement, and concrete test-fixing is the unit of “progress.” This contrasts sharply with population-based evolution, in which a rising mean metric may conceal numerous regressions or untraceable trade-offs. By centering gating on P→F and F→P at the example level, AgentDevel enforces:

• Exceptional sensitivity to new, hard-to-diagnose failures.
• Explicit, auditable attribution of fixes (F→P) to intended changes.
• Statistical and semantic non-regression, minimizing the rate $\rho_t^{\mathrm{P2F}}$.

This design yields improvement trajectories that are stable, easily audited, and reproducible (Zhang, 8 Jan 2026).

3. Mechanized Flip-Centered Gating Algorithm

The release pipeline operates as follows (in LaTeX-like pseudocode from (Zhang, 8 Jan 2026)):

Given: b_t, b_t^{RC}, D_train, p_t(x), p_t^{RC}(x), I_t // Compute flip sets P2F_t = {x in D_train | p_t(x) = 1 and p_t^{RC}(x) = 0} F2P_t = {x in D_train | p_t(x) = 0 and p_t^{RC}(x) = 1} // Compute flip rates (for reporting) rho^{P2F}_t = |P2F_t| / (|{x: p_t(x)=1}| + epsilon) rho^{F2P}_t = |F2P_t| / (|{x: p_t(x)=0}| + epsilon) // Release decision Accept_t = G( ... ) if Accept_t == 1: b_{t+1} <- b_t^{RC} else: b_{t+1} <- b_t

Gate $G$ typically combines simple thresholds:

• Reject if $|\mathrm{P2F}_t| > \tau_{\rm reg}$ or $\rho_t^{\mathrm{P2F}} > \tau_{\rm reg}$
• Require $|\mathrm{F2P}_t| \ge \tau_{\rm fix}$
• Require strong alignment (as judged by LLM critic) between F→P fixes and stated intent $\mathcal{I}_t$

All flips and accept/reject decisions are logged for audit.

4. Empirical Evaluation and Case Analysis

Empirical evaluation on execution-heavy benchmarks such as StableToolBench demonstrates that flip-centered gating maintains P→F regression rates under 0.7% in accepted releases, rejecting iterations where P→F spikes to 4%. For example, in an 11-iteration test set (Table 2, (Zhang, 8 Jan 2026)):

| Iteration | Gate | |F2P| | |P2F| | $\rho^{P2F}_t$ | Frac. good flips (FTP/P2P) | |-----------|-------|-------|-------|----------------|-----------------------| | 1 | Acc. | 38 | 4 | 0.006 | 0.12/0.98 | | 3 | Rej. | 42 | 28 | 0.040 | 0.28/0.93 | | ... | ... | ... | ... | ... | ... |

On WebArena, the absence of flip gating increases P→F rate from 3.1% to 14.8% and yields multiple “bad releases,” while full AgentDevel maintains zero such regressions (Zhang, 8 Jan 2026).

5. Practical Implementation and Limitations

AgentDevel is agnostic to the nature of the pass/fail signal: whenever programmatic graders $g(\hat y, \tau)$ exist, they are used; otherwise, an implementation-blind LLM critic provides verdicts, potentially at some cost in noise or bias. Flip-centered analysis requires rerunning all examples to detect new flips, leading to non-trivial computational overhead. Threshold calibration for $\tau_{\rm reg}$, $\tau_{\rm fix}$, and intent alignment is context- and deployment-specific—there is no universal optimal setting. Mitigation strategies include:

• Versioning and logging all flip sets, intents, and gating actions for full auditability.
• Documenting RC intents and verifying flip alignment.
• Setting denominator stabilization constants (e.g., $\epsilon = 10^{-6}$) in $\rho^{P2F}_t$ to avoid singularities.

6. Broader Context and Comparisons

AgentDevel’s flip-centered gating should be contrasted with population-based and self-refining agent improvement, which typically optimize aggregate statistics using evolutionary search or internal LLM editing, often leading to volatile or non-auditable agent histories. By instead enforcing a developer-style release discipline, AgentDevel centralizes quality control and reproducibility.

Within broader LLM agent development, flip-centered gating as realized in AgentDevel is the first approach formalizing per-example regression tracking and intent-linked release gating as primary objectives (Zhang, 8 Jan 2026). This discipline yields stable and trustworthy agent releases, favoring auditability and non-regression guarantees over unconstrained metric gain.

7. Summary Table: Flip-Centered Gating Metrics in AgentDevel

Metric	Definition/Description	Typical Thresholds (Example)
$\mathrm{P2F}_t$	Set of examples: pass $\to$ fail from $b_t$ to $b_t^{RC}$	$< 1\%$ of all passes
$\mathrm{F2P}_t$	Set of examples: fail $\to$ pass from $b_t$ to $b_t^{RC}$	$> \tau_{\rm fix}$ (e.g., 10 fixes)
$\rho^{\mathrm{P2F}}_t$	$|\mathrm{P2F}_t| / (|\{x: p_t(x)=1\}|+\epsilon)$	$< 1\%$
$\rho^{\mathrm{F2P}}_t$	$|\mathrm{F2P}_t| / (|\{x: p_t(x)=0\}|+\epsilon)$	task-dependent
Alignment w/ $\mathcal{I}$	Fraction of F→P flips aligned with RC intent	$> 95\%$ for promotion

This structure enables reproducible, regression-aware LLM agent improvement, with each release artifact accompanied by a full, example-level regression/fix audit trail (Zhang, 8 Jan 2026).