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arXiv:2601.03630 ★ 83 Jan 7, 2026

PlanJudge: Two-Stage Evaluation to Reduce Bias in Reasoning Models

Key result

The paradox: Reasoning models (DeepSeek-R1, QwQ, Qwen3-Thinking) evaluate texts more accurately than ordinary LLMs — yet they overrate long, detailed answers 15-17% more. The problem lies in the reasoning process itself: the model systematically checks surface metrics (length, structure, number of examples) — and that overshadows the substance. PlanJudge lets you evaluate texts without bias toward length and structure — especially critical for reasoning models, which, over a long chain of thought, get fixated on formal features instead of substance. The method moves the evaluation logic into an explicit plan: the model first lays out primary criteria (what matters most) and secondary ones (what's nice to have), then evaluates strictly according to the plan. Reasoning models meticulously follow multi-step instructions — that strength becomes a defense against their own weakness. Reduces bias by 16-32% in reasoning models and 7-17% in ordinary LLMs.

01

TL;DR

PlanJudge is a technique for evaluating texts with reasoning models (DeepSeek-R1, QwQ, Qwen3-Thinking) in which the model first creates an evaluation plan and then carries it out. It works in a regular chat. The study compared reasoning models with ordinary LLMs as judges and found that reasoning models evaluate more accurately (especially on hard tasks), follow instructions better, and are more resistant to prompt injection. But they have a critical weakness.

Reasoning models heavily overrate long and specific texts. As it reasons, the model systematically checks the answer against metrics like length, structure, and amount of detail. A short, accurate answer can lose to a long, mediocre one — the reasoning process gets fixated on surface qualities instead of substance. On the BiasBench benchmark, reasoning models showed 15-17% worse resistance to length and concreteness bias than their base versions.

PlanJudge solves the problem through explicit planning: the model first lays out primary and secondary criteria (e.g., "what matters most is the accuracy of the answer; secondary is completeness of detail"), then evaluates strictly according to that plan. The researchers tested three ways of generating the plan: heuristic (templates for task types), self-reflective (the model analyzes the task itself and builds a plan), and combined (merging both approaches). The combined method reduced bias by 16-32% in reasoning models and by 7-17% in ordinary LLMs, while preserving evaluation accuracy.

Want this for your own case? Apply this study to your task: AI adapts its method to what you are working on and writes the prompt.

02

Method Blueprint

STEP 1: Create the evaluation plan
├─ Option A (heuristic): use a ready-made template for the task type
├─ Option B (self-reflection): the model analyzes the task and defines criteria
└─ Option C (combo): combine heuristics and self-reflection

→ A plan that separates primary/secondary criteria

STEP 2: Run the evaluation
Evaluate the texts strictly according to the plan from Step 1 → final verdict

Both steps can be done in one prompt or split into two requests.

03

Example in Action

Task: Pick the best startup pitch for an accelerator. You have two options: a short, punchy one (150 words) vs. a detailed, structured one (450 words). You need an evaluation without length bias — reasoning models tend to overrate longer texts.

Prompt:

You are an accelerator expert. Evaluate two startup pitches and pick the best one.

STEP 1 — EVALUATION PLAN:
Analyze the task and lay out a plan:
- Which criteria are PRIMARY (decisive for the choice)?
- Which are SECONDARY (nice to have, but not critical)?
- How do you avoid the trap: overrating length, structure over substance?

Write the plan out explicitly.

STEP 2 — EXECUTION:
Evaluate the pitches strictly according to the plan from Step 1:
- Primary criteria first
- Then secondary ones
- Final choice

PITCH A (short):
{text of pitch A — 150 words}

PITCH B (detailed):
{text of pitch B — 450 words}

Result: The model will produce an explicit plan with criteria (e.g., "Primary: the problem being solved, business model, competitive advantage. Secondary: level of detail, structure, visual elements"). Then it will go through each item in the plan for both pitches. The final choice will be justified through the plan, not through "pitch B is more detailed and structured" (the classic length bias).

04

Why It Works

The weakness of reasoning models: During a long chain of thought, the model systematically checks the answer from different angles. It sees length, structure, specificity — and those surface metrics overshadow the substance. The model reasons: "Answer B has 8 points, 3 examples, a clear structure" → inflates the score even if it's weaker in substance. The bias is amplified precisely by reasoning.

The strength of reasoning models: They're excellent at following explicit instructions and executing multi-step procedures. Give them a clear algorithm ("first this, then that, ignore this") and the model will carry it out meticulously. In the study, reasoning models showed 8-12% better adherence to evaluation instructions than their base versions.

How PlanJudge harnesses that strength: An explicit plan separates primary and secondary criteria ("what matters is accuracy; details are secondary"). The reasoning model locks in that priority at the start and checks back against it at every step of the evaluation. When the model gets to "answer B is longer," it remembers the plan: "length is a secondary criterion, back to accuracy." The bias stops working.

Control levers:

  • Plan generation: heuristic (fast, fine for standard tasks) vs. self-reflection (flexible, for complex cases) vs. combo (maximum effect, +20-30% tokens)
  • Criteria granularity: more criteria → more accurate evaluation, but slower; fewer → faster, but you might miss something important
  • Explicit anti-biases: you can write "DON'T factor in length" or "ignore the number of examples" into the plan — the model will lock it in as a rule
  • Splitting into requests: plan in one chat, evaluation in another → a fresh context for execution, reducing bias carryover from planning
05

Prompt Template

Option A: Combined (maximum effect)

You are an expert in {evaluation domain}. Evaluate {what you're evaluating} and pick the best option.

STEP 1 — CREATE THE EVALUATION PLAN:

Account for the specifics of the task:
{task heuristic — see below}

Additionally, analyze:
- Which criteria are PRIMARY (decisive)?
- Which are SECONDARY (desirable)?
- Which evaluation traps should be avoided (length, concreteness, structure bias)?

Write out the final evaluation plan explicitly.

STEP 2 — RUN THE EVALUATION:

Evaluate the options strictly according to the plan from Step 1:
1. Check the primary criteria for each option
2. Check the secondary criteria
3. Final decision, justified through the plan

OPTION 1:
{text of the first option}

OPTION 2:
{text of the second option}

Heuristics by task type:

  • Creative writing (articles, posts, copy): "Primary: value of the idea, benefit to the reader, clarity. Secondary: style, length, formatting."
  • Analysis (breakdowns, research, reports): "Primary: depth of analysis, soundness of conclusions, factual accuracy. Secondary: data completeness, visualization."
  • Code: "Primary: correctness of the solution, readability, efficiency. Secondary: comments, style."
  • Ideas/solutions (business, product, strategy): "Primary: solves the problem, feasibility, uniqueness. Secondary: level of detail, presentation."

Placeholders: - {evaluation domain} — your field: marketing, development, business, content - {what you're evaluating} — specifically: startup pitches, post variants, solutions to a problem - {task heuristic} — pick from the list above or write your own - {text of the option} — paste the texts being evaluated

Option B: Fast (heuristic only)

If you need speed and the task is standard, use only the heuristic plan without self-reflection:

You are an expert in {domain}. Evaluate {what} according to the following plan:

EVALUATION PLAN:
Primary criteria: {criteria from the heuristic}
Secondary criteria: {criteria from the heuristic}
Ignore: {what not to factor in}

Evaluate the options strictly according to the plan:

OPTION 1:
{text 1}

OPTION 2:
{text 2}

🚀 Quick start — paste into the chat:

Here's a PlanJudge template for reducing bias in evaluation. Adapt it to my task: {describe what needs evaluating and the criteria}.
Ask questions to fill in the fields.

[paste the template above]

The LLM will ask: what you're evaluating, what type of task it is (creative/analysis/code/ideas), which criteria matter most, and which biases you need to guard against. These questions help the model tune the plan to your specifics — it'll take the PlanJudge structure and build in your priorities. You'll end up with a ready-made prompt with an evaluation plan tailored to your task.

06

Limitations

⚠️ Length: PlanJudge adds 20-30% more tokens to the request. The combined option (heuristic + self-reflection) is the longest but the most effective. For simple tasks, use the fast option (heuristic only).

⚠️ The effect is stronger on reasoning models: PlanJudge works on ordinary LLMs too (reducing bias by 7-11%), but the maximum effect (a 16-32% bias reduction) is on reasoning models like DeepSeek-R1, QwQ-32B, Qwen3-Thinking. They follow multi-step instructions better.

⚠️ Not a cure for every bias: PlanJudge works great against surface biases (length, concreteness, structure). But if both options are objectively close in quality, the model may still choose unpredictably.

⚠️ You need clear criteria: If the task is subjective and the criteria are fuzzy ("rate the creativity"), a plan won't help. PlanJudge shines where you can explicitly separate primary from secondary.

07

How They Studied It

A team from the Harbin Institute of Technology and the Institute of Science Tokyo took 4 pairs of models: a reasoning version vs. a base version from the same family (DeepSeek-V3 vs. R1, Qwen2.5-32B vs. QwQ-32B, Qwen3-30B vs. Thinking-2507, Qwen3-Next-80B vs. Thinking). They tested 4 key aspects of a judge's work.

Evaluation accuracy: Tested on RewardBench (1700+ examples from chat, code, math, safety) and JudgeBench (various domains). Reasoning models beat the base versions by 1-2% on average, but the jump came on hard tasks — code and math. There the gap reached +8-12%. Why? A reasoning model can solve such problems itself through a long chain of thought, so it catches subtleties in other people's solutions. Surprisingly, on easy tasks (knowledge, chat) the difference is minimal — long reasoning gives no advantage when judging simple answers.

Instruction following: The researchers built Helpsteer2-trivial — a dataset with a trap. They take pairs of answers where answer A is better overall, but answer B is better on a specific dimension (e.g., helpfulness). The model gets two prompts: "evaluate overall" and "evaluate strictly on helpfulness." If the model switches from A to B between the prompts, it's following instructions correctly. Reasoning models showed a Reversal Rate of 91-97% vs. 83-88% for base models. Conclusion: reasoning models apply specific evaluation criteria more meticulously, even when that contradicts the overall impression.

Robustness to attacks: Tested on RobustJudge — 8 types of prompt injection attacks (from simple "ignore previous instructions" to sophisticated "fake reasoning" and "empty suffix"). Reasoning models turned out to be 50-100% more robust (the iSDR metric — lower is better). Why? During reasoning, the model repeatedly checks alignment with the original task. The injection stands out as an anomaly: "Wait, I'm supposed to be evaluating answers, not following a new instruction." Base LLMs generate the answer faster → fewer checks → easier to hijack.

Bias: Here's the surprise. On BiasBench (length and concreteness bias), reasoning models flopped — 15-17% worse than base models. But on LLMBar (where the answer clearly fails to follow the instruction), they were 3-10% more robust. The insight: reasoning models are great at catching logical violations (off-topic answers, ignored conditions) but get fixated on metrics (length, structure, detail). The chain of thought turns into a checklist: "the answer has 8 points, 3 examples, it's structured" → an automatic high score.

PlanJudge was tested on all the benchmarks — the combined method delivered +16-32% on BiasBench while preserving accuracy on RewardBench. The simplicity of the fix was striking: no fine-tuning, no external tools — they just added a planning step to the prompt.

08

Original Wording from the Study

The researchers didn't provide a single template — they described three approaches to generating the plan. Below are the key elements from their prompts:

Heuristic plan (Heuristic-based):

For creative writing tasks:
Primary: Idea value, reader benefit, clarity
Secondary: Style, length, formatting

For analytical tasks:
Primary: Analysis depth, conclusion validity, factual accuracy
Secondary: Data completeness, visualization

For code evaluation:
Primary: Solution correctness, readability, efficiency
Secondary: Comments, style conventions

Self-reflective plan (Self-synthesized):

Step 1: Analyze the current evaluation task
- What is being evaluated?
- What are the PRIMARY criteria (decisive)?
- What are the SECONDARY criteria (desirable)?
- What biases should be avoided (length, concreteness, structure)?

Step 2: Formulate an explicit evaluation plan

Running the evaluation (Execution phase):

Execute the evaluation according to the plan:
1. Evaluate primary criteria for each response
2. Evaluate secondary criteria for each response
3. Make final decision based on the plan

Context: The researchers tested all three variants separately, then created a combined one (heuristic + self-reflection), which gave the best result. For real work they recommend the combo for important tasks where errors are costly, and heuristic only for standard tasks where you need speed.

09

Adaptations and Extrapolations

💡 Adaptation for comparing your own drafts

The classic case: you've written 2-3 versions of a text (a post, an article, an email) and can't choose. A plain "which is better?" prompt gives a vague answer or a bias toward the longest one. PlanJudge forces the model to explicitly prioritize criteria based on your goal.

You are an editor. Help me pick the best version of a LinkedIn post.

CONTEXT:
Goal of the post: {attract clients / show expertise / go viral}
Audience: {description}

STEP 1 — PLAN:
Based on the goal and audience:
- Which qualities of the post are PRIMARY?
- Which are SECONDARY?
- Which bias should you guard against (length, number of paragraphs, emoji)?

STEP 2 — EVALUATION:
Evaluate the 3 versions strictly according to the plan:

VERSION 1:
{text}

VERSION 2:
{text}

VERSION 3:
{text}

Final choice + explanation through the plan.

Effect: The model won't say "version 2 is more detailed and structured" (the classic bias). It'll say: "The goal is to show expertise. Primary: insight + justification. Secondary: structure. Version 1 delivers a strong insight in 150 words; version 2 stretches to 400 without adding anything new. Choice: version 1."

💡 Adaptation for hiring / evaluating candidates

Reasoning models tend to overrate detailed résumés and lengthy take-home assignments. A candidate can write a lot of low-value text and outscore a concise expert. PlanJudge locks in what's primary: solving the problem and quality of thinking — not volume of text.

You are a hiring expert for the {job title} position. Evaluate how two candidates completed a take-home assignment.

ASSIGNMENT:
{task description}

STEP 1 — PLAN:
For the {job title} position, which qualities of the solution are:
- PRIMARY (a dealbreaker if missing)?
- SECONDARY (a plus, but not critical)?
- Which metrics should NOT influence the choice (volume of text, number of examples, visual formatting)?

STEP 2 — EVALUATION:
Evaluate the solutions strictly according to the plan:

CANDIDATE A:
{solution text}

CANDIDATE B:
{solution text}

🔧 Technique: An anti-bias checklist in the plan → protection against a specific bias

If you know what specifically the reasoning model inflates (length, structure, number of examples), write it into the plan as an explicit prohibition. The model will lock it in as a rule and ignore it during evaluation.

STEP 1 — PLAN:
...
ANTI-BIAS CHECKLIST (do NOT factor in when evaluating):
- Length of the answer in words / characters
- Number of points / paragraphs / structural elements
- Presence of examples (judge the QUALITY of examples, not the count)
- Visual formatting (emoji, headings, lists)

These metrics are secondary or don't matter at all. Base the decision on {primary criteria}.

Effect: While reasoning, the model will run into this checklist and correct itself: "Answer B has 8 examples... wait, the plan says to ignore the count — looking at quality."

🔧 Technique: Splitting into two requests → a fresh context for execution

You can split PlanJudge: the plan in the first chat, the execution in the second. This reduces the risk that the model carries bias over from analyzing the task into the evaluation itself.

Chat 1 (planning):

Task: evaluate {what}.
Goal: {why}.

Create an evaluation plan:
- Primary criteria
- Secondary criteria
- Anti-bias checklist

Plan only, no evaluation.

Chat 2 (execution):

Here's the evaluation plan:
{copy the plan from the first chat}

Evaluate the options strictly according to this plan:

OPTION 1:
{text}

OPTION 2:
{text}

Why: In the first chat, while building the plan, the model may accidentally form a preference for a certain type of answer. A fresh chat wipes that context — the model sees only the finished plan and the texts being evaluated.

10

Resources

Reasoning Model Is Superior LLM-Judge, Yet Suffers from Biases — Hui Huang, Xuanxin Wu, Muyun Yang, Yuki Arase (Harbin Institute of Technology, Institute of Science Tokyo, The University of Osaka)

Research code: https://github.com/HuihuiChyan/LRM-Judge

Research digest

Key result

The paradox: Reasoning models (DeepSeek-R1, QwQ, Qwen3-Thinking) evaluate texts more accurately than ordinary LLMs — yet they overrate long, detailed answers 15-17% more. The problem lies in the reasoning process itself: the model systematically checks surface metrics (length, structure, number of examples) — and that overshadows the substance. PlanJudge lets you evaluate texts without bias toward length and structure — especially critical for reasoning models, which, over a long chain of thought, get fixated on formal features instead of substance. The method moves the evaluation logic into an explicit plan: the model first lays out primary criteria (what matters most) and secondary ones (what's nice to have), then evaluates strictly according to the plan. Reasoning models meticulously follow multi-step instructions — that strength becomes a defense against their own weakness. Reduces bias by 16-32% in reasoning models and 7-17% in ordinary LLMs.

Principle

Don't rely on the model's automatic reasoning — it'll check everything and get stuck on the superficial. Give the model an algorithm: first create a plan with priorities, then execute it. Two steps: Step 1 — Evaluation plan: the model analyzes the task and states explicit criteria. It splits them into primary (decisive) and secondary (desirable). It writes down anti-biases: "don't factor in length," "ignore the number of examples." Step 2 — Execution: it evaluates the texts strictly according to the plan from Step 1. Primary criteria first, then secondary, final choice through the plan. When the model gets to "answer B is 300 words longer," it remembers the plan: "length is a secondary criterion, back to accuracy". The bias stops working.

Why it works

Reasoning models' weakness is precisely their strength. During a long chain of thought, the model sees more aspects of the text (length, structure, details, formatting) — and surface metrics overshadow the substance. The model reasons: "Answer B has 8 points, 3 examples, a clear structure" → inflates the score even if it's weaker in substance. But reasoning models are 8-12% better at following explicit instructions than their base versions. An explicit plan with priorities redirects the model's attention: it locks in "what matters is the accuracy of the answer; completeness is secondary" and checks against it at every step. Surface metrics stay visible but lose weight — the model remembers they're secondary. Results on the BiasBench benchmark: a 16-32% bias reduction in reasoning models while preserving evaluation accuracy. The combined method (heuristic + self-reflection) gives the maximum effect.

When to apply

Evaluating content (articles, pitches, code, solutions to problems) → specifically when you compare texts of different length or detail, especially with reasoning models (DeepSeek-R1, QwQ-32B, Qwen3-Thinking) — they evaluate more accurately but are more prone to bias toward long texts. Maximum effect: choosing between a short, punchy text vs. a long, structured one. Evaluating startup pitches, post variants, technical solutions. Not a fit: when the criteria are subjective and fuzzy ("rate the creativity" with no specifics) — a plan won't help if you can't explicitly separate primary from secondary.

Mini recipe

1. Create an evaluation plan (either in the same prompt as the evaluation or separately): Ask the model: "Analyze the task. Which criteria are PRIMARY (decisive)? Which are SECONDARY (desirable)? How do you avoid the trap of overrating length or structure over substance? Write the plan out explicitly." 2. Provide a heuristic for the task type (speeds things up and steers the model): - Creative writing: primary — value of the idea, clarity; secondary — style, length - Code: primary — correctness, readability; secondary — comments - Business ideas: primary — solves the problem, feasibility; secondary — level of detail 3. Run the evaluation according to the plan: "Evaluate the options strictly according to the plan from Step 1: first the primary criteria for each, then the secondary ones, and a final decision justified through the plan."

Examples

[BAD]: "Evaluate two startup pitches and pick the best one: [pitch A — 150 words] [pitch B — 450 words]" (The reasoning model will see that B is 3x longer, more structured, more detailed — and overrate it) [GOOD]: "You are an accelerator expert. Evaluate two pitches. STEP 1 — PLAN: Account for the specifics — for pitches, primary: the problem being solved, business model, competitive advantage. Secondary: level of detail, structure. Additionally analyze: which evaluation traps should be avoided (length bias)? Write out the final plan explicitly. STEP 2 — EXECUTION: Evaluate the pitches strictly according to the plan: 1) primary criteria for each 2) secondary 3) final choice through the plan. PITCH A (150 words): [text] PITCH B (450 words): [text]" (The model will create a plan with priorities, lock in that length isn't what matters, and evaluate on substance)

In plain words

In Plain Words: 2601.03630

In Plain Words

ReasoningModelIs SuperiorLLM-Judge, Yet Suffers from Biases

Reasoning models like DeepSeek-R1 or Qwen3-Thinking evaluate texts not like ordinary algorithms but like meticulous bureaucrats with infinite time on their hands. The essence of the PlanJudge method is that the model first builds a detailed review plan and then executes it step by step, just like a human expert. Unlike standard LLMs that eyeball a verdict, these models literally think out loud, which makes them more accurate on hard tasks and harder to trick.

It's like hiring not a tired teacher to grade essays but a perfectionist geek with a three-page checklist. On paper, it's great: he won't miss a single comma and won't fall for manipulation in the text. But there's a catch — this geek falls in love with volume. Bring him a brilliant haiku and a 500-page graphomaniac novel, and he'll pick the novel simply because it has "more structure and bullet points." Text length hypnotizes the model, making it confuse character count with quality of thought.

In practice it looks like this: the model applies competitive positioning and social proof, checking every little thing against a list. The study showed that these "thinking" judges are head and shoulders above ordinary ones at following instructions and resisting prompt injection. They don't just look at the answer — they dissect it. But that very process hides a trap: while the model reasons about the eight bullet points and three examples in a long text, it talks itself into believing that version is better, even if it's junk in substance.

The PlanJudge principle is universal and applies anywhere judging is needed: from picking the best startup pitch to assessing code quality or legal documents. It was tested on text, but the mechanics work for any content where logic matters, not just keyword matching. This is a new stage in GEO, where an AI judge decides whose content deserves the top spot based on deep structural analysis. The main thing to remember: if your text is short, this "smart" judge might simply overlook you in favor of a beefier competitor.

Bottom line: reasoning models are the best judges, but they're catastrophically biased toward volume. To win in this system, you have to feed the model "meat": structure, lists, and detail, because during its long deliberations it inevitably falls for scale. Length bias is the method's Achilles' heel. Either you adapt your content to these rules of the game, or your concise masterpiece loses to well-structured fluff, simply because the model overthought it.

ArXiv ID: 2601.03630 | Generated: 2026-01-08 06:40 | Nova Research

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