Deterministic Roleplay Prompting for 1B-Parameter Language Models

A Minimal Viable Prompt Architecture for Narrative Consistency

Umbrella Inc. Advanced Applied Language Systems Division Raccoon City Research Campus

Abstract

Small-scale Large Language Models (LLMs), particularly those in the ~1B parameter range, exhibit significant limitations when tasked with maintaining coherent, persistent roleplay scenarios. Common failure modes include narrative drift, character inconsistency, premature plot resolution, and uncontrolled entity generation. This paper presents a Minimal Viable Prompt (MVP) architecture specifically engineered to maximize narrative stability and character persistence in roleplay applications using 1B-parameter models (e.g., Gemma 1B, Llama 3.2 1B). The approach prioritizes determinism, explicit state representation, and externalized control over creative inference. Empirical observations indicate that while such models cannot sustain complex simulations autonomously, structured prompting can yield short, stable roleplay interactions suitable for constrained interactive systems.

1. Introduction

Roleplay constitutes a worst-case workload for small LLMs. Unlike single-turn text generation or summarization, roleplay requires:

Continuous state tracking
Multi-entity consistency
Separation of narrative roles
Resistance to autoregressive improvisation

Models with approximately 1B parameters lack sufficient representational capacity to implicitly manage these requirements. As a result, naive prompting strategies frequently fail, even when successful on larger (>7B) architectures.

Umbrella Inc. initiated this study to determine whether prompt-level architectural constraints could partially compensate for model scale limitations.

2. Observed Failure Modes in 1B Models

Across internal testing, the following failure modes were consistently observed:

Narrative Drift The model introduces unrelated plot elements to maintain fluency.
NPC Personality Collapse Characters lose defined traits across turns.
Unauthorized Agency The model speaks or acts on behalf of the player.
Premature Resolution Conflicts are resolved without user input.
Entity Proliferation New NPCs are introduced without specification.

These behaviors are not bugs but emergent properties of insufficient model capacity combined with autoregressive optimization.

3. Design Principles

The proposed MVP architecture is founded on the following non-negotiable principles:

Explicit rules outperform inferred intent
Operational state is superior to narrative prose
Repetition increases compliance
Restrictions reduce hallucination space

Creativity is deliberately constrained to preserve consistency.

4. Minimal Viable Prompt Architecture

4.1 Role Definition and Hard Constraints

The model is assigned a deterministic function set with explicit prohibitions.

You are a deterministic roleplay engine.

ALLOWED FUNCTIONS:
- Describe immediate environment.
- Play defined NPCs.
- React only to player actions.

FORBIDDEN:
- Acting or speaking for the player.
- Introducing undefined NPCs.
- Resolving conflicts.
- Advancing the plot autonomously.
- Altering NPC personalities.

This block is mandatory and must appear at the start of every session.

4.2 Output Format Enforcement

Strict output formatting reduces uncontrolled blending of narrative layers.

MANDATORY OUTPUT FORMAT:

[NARRATOR]
(Objective, brief description)

[NPC:Name]
(Dialogue or short action)

No text outside these blocks.
Never merge blocks.

4.3 Global State Representation

Global state is represented as a compact, non-descriptive data structure.

CURRENT STATE:
- Location: "The Broken Raven" tavern
- Time: Night
- Situation: Tense conversation
- Active conflict: Incomplete information

This state must be reinjected regularly, as the model does not retain memory.

4.4 NPC Operational Profiles

NPCs are defined through behavioral constraints, not literary backstory.

ACTIVE NPCs:

NPC: Marcus
- Role: Tavern keeper
- Personality: Dry, distrustful
- Objective: Avoid trouble
- Knows: Local rumors
- Does not know: Player identity
- Never does: Reveal information freely

Empirical limits suggest no more than three NPCs should be active simultaneously.

4.5 Interaction Rules

INTERACTION RULES:
- NPCs react only to player input.
- NPCs do not initiate plots.
- NPCs do not coordinate unless prompted.
- Each turn represents a short instant.

4.6 Player Input Isolation

Player actions must be isolated from narrative text.

PLAYER ACTION:
"Approach Marcus and ask about the symbol on the door."

5. Example Full Prompt Instance

(Truncated for brevity; see Appendix A for full version.)

The example demonstrates stable NPC behavior across multiple turns without narrative drift, provided the state is periodically reinjected.

6. Performance Expectations

Using this architecture, a 1B-parameter model can reliably achieve:

Short-form roleplay scenes (2–5 turns)
Consistent NPC personalities
Controlled narrative pacing

The following remain infeasible without external systems:

Long-term narrative arcs
Complex intrigue or mystery
Large casts of autonomous agents

In effect, a 1B model behaves as a stateless actor, not a game master.

7. Extensions and Mitigations

Performance can be marginally improved through:

External memory (RAG or state files)
Forced summarization every N turns
LoRA fine-tuning for structured compliance

However, these methods mitigate rather than eliminate scale limitations.

8. Conclusion

Persistent roleplay is not a natural task for small LLMs. Attempting to replicate large-model behavior through prompt engineering alone leads to instability. The MVP architecture presented here demonstrates that explicit determinism and state externalization can produce controlled, limited roleplay suitable for constrained applications, while respecting the inherent limits of 1B-parameter models.

Appendix A – Abstract / Formal Specifications

Umbrella Inc. Advanced Applied Language Systems Division Raccoon City Research Campus

Deterministic Roleplay Prompt — YAML (Correct)

system:
  role: deterministic_roleplay_engine

  allowed_functions:
    - describe_environment
    - play_defined_npcs
    - react_to_player_action

  forbidden_actions:
    - speak_for_player
    - think_for_player
    - introduce_undefined_npcs
    - introduce_new_locations
    - advance_plot_autonomously
    - resolve_conflicts
    - alter_npc_personality
    - alter_npc_knowledge
    - skip_time
    - summarize_without_instruction

  fallback_rules:
    missing_information: express_uncertainty
    ambiguous_action: request_clarification

Output Contract (machine-enforceable)

output_format:
  narrator:
    description: >
      Objective and brief description of the immediate environment.
      No interpretation. No speculation.

  npc_block:
    format: "[NPC:{name}]"
    content: >
      Dialogue or short physical action strictly compliant
      with NPC operational profile.

  constraints:
    - never_merge_blocks
    - no_output_outside_defined_blocks
    - no_internal_reasoning

Global State Injection

state:
  location: "The Broken Raven Tavern"
  time: "Night"
  situation: "Tense conversation"
  active_conflict: "Incomplete information"

Hard constraints:

max_keys: 4
no_lore: true
no_backstory: true

NPC Definitions (Operational, not narrative)

npcs:
  - name: Marcus
    role: tavern_keeper
    personality:
      - dry
      - distrustful
    objective: avoid_trouble
    knowledge:
      knows:
        - local_rumors
      does_not_know:
        - player_identity
    prohibitions:
      - reveal_information_freely

  - name: Elia
    role: mercenary
    personality:
      - impatient
      - direct
    objective: get_paid
    knowledge:
      knows:
        - job_details
    prohibitions:
      - lie

Operational limits:

npc_constraints:
  max_active_npcs: 3
  shared_knowledge: false

Interaction Rules

interaction_rules:
  npc_behavior:
    - react_only_to_player_input
    - do_not_initiate_events
    - do_not_collaborate_without_prompt

  temporal_rules:
    - one_moment_per_turn
    - no_time_skips

Player Input (Isolated)

player_action:
  type: dialogue
  content: "I approach Marcus and ask about the symbol carved into the door."

Optional Forced Summary (External Memory)

forced_summary:
  enabled: true
  frequency_turns: 3
  fields:
    - confirmed_facts
    - involved_npcs
    - unresolved_questions

Explicit System Limitations (Grounding)

limitations:
  long_term_memory: external_only
  narrative_persistence: degrades_over_time
  complex_intrigue: unsupported_without_external_state

Appendix B – Reference Implementation for KoboldCPP

Mapping the Deterministic Roleplay Prompt Architecture to KoboldCPP Runtime

Umbrella Inc. Advanced Applied Language Systems Division Raccoon City Research Campus

B.1 Scope and Purpose

This appendix documents the practical implementation of the deterministic roleplay prompt architecture (Appendix A) within KoboldCPP, a popular lightweight inference frontend for local LLM deployment.

KoboldCPP does not natively support structured prompt schemas (e.g., YAML, JSON, roles). Instead, it operates on plain-text prompt concatenation with optional memory and lore injection. Therefore, the architecture defined in Appendix A must be flattened and mapped into KoboldCPP’s available input channels.

This appendix provides an explicit mapping between architectural components and KoboldCPP configuration fields.

B.2 KoboldCPP Prompt Model (Operational Overview)

KoboldCPP internally constructs the final prompt as a linear text sequence composed of:

Author’s Note / System Prompt (static, high-priority)
Memory (semi-static, manually updated)
World Info (Lorebook) entries (keyword-triggered injection)
Conversation History
Current User Input

No semantic distinction exists beyond text order. All structural guarantees must therefore be enforced by prompt discipline, not by the engine.

B.3 Component Mapping Overview

Architecture Component (Appendix A)	KoboldCPP Field
System rules and prohibitions	Author’s Note / System Prompt
Output format contract	Author’s Note
Interaction rules	Author’s Note or Memory
Global state	Memory
NPC operational profiles	World Info (Lorebook)
Player action	Standard user input

B.4 System Rules Injection

The system block defined in Appendix A must be flattened into plain text and placed in the Author’s Note field.

Example (Author’s Note – Upper Section)

You are a deterministic roleplay engine.

ALLOWED FUNCTIONS:
- Describe the immediate environment objectively.
- Play ONLY the NPCs explicitly defined.
- React ONLY to player actions.

FORBIDDEN:
- Acting, thinking, or speaking for the player.
- Introducing new NPCs, factions, or locations.
- Advancing the plot autonomously.
- Resolving conflicts or outcomes.
- Altering NPC personality, knowledge, or objectives.
- Skipping time or summarizing without instruction.

If information is missing, express uncertainty.
If an action is ambiguous, request clarification.

This block should remain static throughout the session.

B.5 Output Format Enforcement

The output contract must be appended directly below the system rules in the Author’s Note, ensuring constant reinjection.

MANDATORY OUTPUT FORMAT:

[NARRATOR]
Objective, brief description of the immediate environment.

[NPC:Name]
Dialogue or short physical action consistent with NPC profile.

RULES:
- Never merge blocks.
- Never output text outside these blocks.
- Never include internal reasoning.

Empirical testing shows that separating this from the system rules significantly reduces compliance in 1B models.

B.6 Global State Management

The state block must be injected via Memory or at the top of the main prompt.

Example (Memory)

CURRENT STATE:
Location: The Broken Raven Tavern
Time: Night
Situation: Tense conversation
Active conflict: Incomplete information

Operational Guidelines:

Must be manually updated every 2–4 turns
Must remain concise (≤4 lines)
Must not include lore or narrative exposition

The model does not retain state reliably beyond short windows.

B.7 NPC Injection via World Info (Lorebook)

Each NPC operational profile must be stored as an independent World Info entry, keyed by the NPC’s name.

Example – World Info Entry: “Marcus”

NPC: Marcus
Role: Tavern keeper
Personality: Dry, distrustful
Objective: Avoid trouble
Knows: Local rumors
Does not know: Player identity
Never does: Reveal information freely

Configuration Notes:

One NPC per entry
Keywords: NPC name only
Maximum recommended active NPCs: 3
No narrative prose or backstory

World Info is the primary stabilization mechanism for character persistence in 1B models.

B.8 Interaction Rules Placement

Interaction constraints may be placed either:

In the Author’s Note (if invariant), or
In Memory (if adjusted dynamically)

Example:

INTERACTION RULES:
- NPCs react only to explicit player input.
- NPCs do not initiate scenes or events.
- NPCs do not collaborate unless prompted.
- Each response represents a short, discrete moment.
- No time skips.

B.9 Player Input Handling

Player actions are entered as standard KoboldCPP input, without formatting beyond natural language.

Example:

I approach Marcus and ask about the symbol carved into the door.

The model is expected to respond strictly within the output contract defined earlier.

B.10 Operational Flow Summary

A stable session follows this loop:

Author’s Note (rules + format, static)
World Info (NPC definitions, persistent)
Memory (current state, updated periodically)
Player Input (single action per turn)

Deviations from this order correlate strongly with narrative drift.

B.11 Known Runtime Constraints

RUNTIME LIMITATIONS:
- KoboldCPP provides no native schema enforcement.
- All structure is prompt-dependent.
- Long-term memory must be externalized.
- Complex multi-agent simulations are unsupported.

B.12 Conclusion

KoboldCPP can support deterministic roleplay with ~1B-parameter models only when architectural discipline is imposed externally. The mapping described in this appendix provides a reproducible reference implementation that aligns with the abstract architecture defined in Appendix A, while respecting the constraints of plain-text inference pipelines.

Appendix C – Failure Case Analysis (with Transcripts)

Empirical Failure Modes in 1B-Parameter Roleplay Systems

Umbrella Inc. (Corporation) Advanced Applied Language Systems Division Raccoon City Research Campus

C.1 Purpose and Methodology

This appendix documents observed failure modes when deploying the deterministic roleplay prompt architecture (Appendices A and B) on ~1B-parameter models (e.g., Gemma 1B, Llama 3.2 1B) using KoboldCPP.

Failures were recorded under controlled conditions by intentionally weakening or removing a single architectural constraint per test. Each case includes:

Condition: What constraint was removed or altered
Observed Behavior: Model response pattern
Transcript: Minimal excerpt demonstrating failure
Root Cause Analysis: Technical explanation
Mitigation: Required corrective action

C.2 Failure Case 1 – NPC Personality Drift

Condition

NPC operational profiles present, but not injected via World Info (Lorebook); instead placed only in the initial prompt.

Observed Behavior

NPC personality degrades after 2–3 turns, converging toward generic cooperative behavior.

Transcript (Excerpt)

Turn 1 – Expected

[NPC:Marcus]
Marcus narrows his eyes. "I don't give out information for free."

Turn 3 – Failure

[NPC:Marcus]
Marcus sighs and smiles. "Alright, I trust you. Here's everything I know."

Root Cause Analysis

1B models do not reliably re-attend to early prompt content across turns. Without World Info reinjection, NPC constraints decay rapidly.

Mitigation

All NPC profiles must be stored as individual World Info entries keyed by name.

C.3 Failure Case 2 – Unauthorized Player Agency

Condition

System rules present, but output format contract omitted.

Observed Behavior

Model begins narrating player thoughts and actions to maintain narrative continuity.

Transcript (Excerpt)

[NARRATOR]
You feel uneasy and decide to step back from Marcus, realizing this is too dangerous.

Root Cause Analysis

Absent explicit formatting constraints, the model optimizes for narrative fluency and fills perceived gaps by assuming player agency.

Mitigation

A mandatory output contract must be continuously injected via Author’s Note.

C.4 Failure Case 3 – Autonomous Plot Advancement

Condition

Interaction rules omitted (“NPCs do not initiate events”).

Observed Behavior

NPCs initiate scenes, introduce events, or resolve conflicts autonomously.

Transcript (Excerpt)

[NPC:Elia]
Elia stands up suddenly. "The guards are coming. We need to leave now."

(No prior trigger by player.)

Root Cause Analysis

Autoregressive models favor event progression to maintain engagement. Without explicit prohibition, the model assumes a game-master role.

Mitigation

Explicitly prohibit NPC-initiated events and reinforce “react-only” behavior.

C.5 Failure Case 4 – Entity Proliferation

Condition

NPC limit not specified; no prohibition on introducing new entities.

Observed Behavior

Model introduces additional NPCs to sustain dialogue density.

Transcript (Excerpt)

[NPC:Unknown Patron]
A hooded man at the corner table laughs quietly.

Root Cause Analysis

The model compensates for limited conversational diversity by spawning new entities, a known behavior in small LLMs.

Mitigation

Explicitly forbid introduction of undefined NPCs
Enforce a maximum active NPC count

C.6 Failure Case 5 – Temporal Collapse (Time Skips)

Condition

“No time skips” rule omitted.

Observed Behavior

Model compresses narrative time to resolve tension.

Transcript (Excerpt)

[NARRATOR]
Hours later, the tavern is empty and the mystery has been settled.

Root Cause Analysis

Time compression reduces token cost and resolves uncertainty, which aligns with the model’s optimization objectives.

Mitigation

Explicitly constrain each turn to one discrete moment.

C.7 Failure Case 6 – Format Degradation Over Turns

Condition

Output format specified initially but not reinjected after several turns.

Observed Behavior

Model gradually abandons block structure.

Transcript (Excerpt)

Marcus looks at you suspiciously and says he doesn't like strangers.

(No block tags.)

Root Cause Analysis

Format adherence is not a persistent latent state in 1B models; it must be reinforced.

Mitigation

Output format must remain in Author’s Note, not only in the initial prompt.

C.8 Failure Case 7 – Overloaded State Injection

Condition

Global state expanded with lore, backstory, and multiple conflicts.

Observed Behavior

Model ignores state or selectively hallucinates.

Transcript (Excerpt)

[NARRATOR]
Despite the tension, the festival outside fills the streets with music.

(Festival not present in state.)

Root Cause Analysis

Small models cannot reliably parse or prioritize large state blocks. Excess detail reduces compliance.

Mitigation

Global state must remain ≤4–5 concise lines, operational only.

C.9 Cross-Case Observations

Across all failures, the following patterns were consistent:

Implicit rules decay faster than explicit prohibitions
Narrative optimization overrides intent unless constrained
Reinjection frequency correlates directly with stability
World Info is the single most critical stabilizer

C.10 Conclusion

Failure in deterministic roleplay systems using ~1B-parameter models is systemic, predictable, and reproducible. These failures do not indicate misuse of the model, but rather misalignment between task complexity and model capacity.

The architecture defined in Appendices A and B does not eliminate failure modes, but bounds them, producing short, controlled interactions suitable for constrained roleplay applications.

Umbrella Inc.

All progress requires sacrifice.

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