# Inference Cost Optimization Plan

**Goal**: Reduce LLM inference costs without quality loss using OpenClaw's built-in configuration knobs + smarter subagent model selection. No code changes to OpenClaw — config-only, fully upstream-compatible.

**Date**: 2026-03-05
**Status**: Planning

---

## Current State

| Item | Value |
|------|-------|
| Main session model | `litellm/copilot-claude-opus-4.6` (via GitHub Copilot) |
| Default agent model | `litellm/copilot-claude-sonnet-4.6` |
| Prompt caching | **NOT SET** (no `cacheRetention` configured) |
| Context pruning | **NOT SET** (no `contextPruning` configured) |
| Heartbeat | 30m (main agent only) |
| Subagent model | Inherits session model (expensive!) |
| Free models available | `zai/glm-4.7`, `zai/glm-4.7-flash`, `zai/glm-4.7-flashx`, `zai/glm-5` (all $0) |
| Copilot models | Flat-rate via GitHub Copilot subscription (effectively $0 marginal cost per token) |

### Cost Structure
- **Copilot models** (litellm/copilot-*): Covered by GitHub Copilot subscription — no per-token cost, but subject to rate limits and quotas. Using Opus when Sonnet suffices wastes quota.
- **ZAI models** (zai/glm-*): Free tier, no per-token cost. Quality varies by task type.
- The real "cost" is: (a) Copilot quota burn on expensive models, (b) latency, (c) quality risk on cheaper models.

---

## Phase 1: Enable Prompt Caching

**What**: Configure `cacheRetention` on Anthropic-backed models so repeated system prompts and stable context get cached by the provider.

**Why**: Our system prompt (AGENTS.md + SOUL.md + USER.md + TOOLS.md + IDENTITY.md + HEARTBEAT.md + skills list) is large and mostly static. Without caching, every turn reprocesses ~15-20k tokens of identical prefix. With caching, subsequent turns pay ~10% for cached tokens (Anthropic pricing).

**Config change** (`~/.openclaw/openclaw.json`):
```json
{
  "agents": {
    "defaults": {
      "models": {
        "litellm/copilot-claude-opus-4.6": {
          "params": {
            "cacheRetention": "long"
          }
        },
        "litellm/copilot-claude-sonnet-4.6": {
          "params": {
            "cacheRetention": "long"
          }
        },
        "litellm/copilot-claude-opus-4.5": {
          "params": {
            "cacheRetention": "long"
          }
        },
        "litellm/copilot-claude-sonnet-4.5": {
          "params": {
            "cacheRetention": "long"
          }
        },
        "litellm/copilot-claude-haiku-4.5": {
          "params": {
            "cacheRetention": "short"
          }
        }
      }
    }
  }
}
```

**Verification**:
1. After applying, check `/status` or `/usage full` for `cacheRead` vs `cacheWrite` tokens.
2. Enable cache trace diagnostics temporarily:
   ```json
   { "diagnostics": { "cacheTrace": { "enabled": true } } }
   ```
3. First turn will show high `cacheWrite` (populating cache). Subsequent turns should show high `cacheRead` with much lower `cacheWrite`.
4. Target: >60% cache hit rate within 2-3 turns of a session.

**Risk**: Zero. Caching doesn't change outputs — it's purely a provider-side optimization.

**Expected impact**: 40-60% reduction in input token processing cost for sessions with multiple turns.

---

## Phase 2: Heartbeat Cache Warming

**What**: Align heartbeat interval to keep the prompt cache warm across idle gaps.

**Why**: Anthropic's `long` cache retention is ~1 hour TTL. Our current heartbeat is 30m, which is already well under the TTL — good. But we should ensure the heartbeat is a lightweight keep-warm that doesn't generate expensive cache writes.

**Config change** (`~/.openclaw/openclaw.json`):
```json
{
  "agents": {
    "defaults": {
      "heartbeat": {
        "every": "55m"
      }
    },
    "list": [
      {
        "id": "main",
        "heartbeat": {
          "every": "25m"
        }
      }
    ]
  }
}
```

**Rationale**:
- Main agent: keep at 25m (well within 1h TTL, ensures cache stays warm during active use)
- Other agents (claude, codex, copilot, opencode): 55m default (just under 1h TTL, minimal quota burn when idle)
- If an agent is rarely used, its heartbeat won't fire (disabled agents skip heartbeat)

**Verification**:
1. After a 30-minute idle gap, check that the next interaction shows `cacheRead` (not all `cacheWrite`).
2. Monitor heartbeat token cost via `/usage full` on a heartbeat response.

**Risk**: Low. Slightly more frequent heartbeat = slightly more baseline token usage, but the cache savings on real interactions outweigh this.

**Expected impact**: Maintains the Phase 1 cache savings across idle periods instead of losing them after TTL expiry.

---

## Phase 3: Context Pruning

**What**: Enable `cache-ttl` context pruning so old tool results and conversation history get pruned after the cache window expires.

**Why**: Long sessions accumulate tool results, file reads, and old conversation turns that bloat the context. Without pruning, post-idle requests re-cache the entire oversized history. Cache-TTL pruning trims stale context so re-caching after idle is smaller and cheaper.

**Config change** (`~/.openclaw/openclaw.json`):
```json
{
  "agents": {
    "defaults": {
      "contextPruning": {
        "mode": "cache-ttl",
        "ttl": "1h"
      }
    }
  }
}
```

**Rationale**:
- `cache-ttl` mode: prunes old tool-result context after the cache TTL expires
- `ttl: "1h"`: matches Anthropic's `long` cache retention window
- After 1h of no interaction, old tool results and conversation history are pruned, so the next request re-caches a smaller context

**Verification**:
1. Use `/context list` or `/context detail` to check context size before and after pruning.
2. After a >1h idle gap, verify the context window is smaller than before the gap.
3. Ensure no critical context is lost — compaction summaries should preserve key information.

**Risk**: Low-medium. Pruning removes old tool results, which means the model can't reference exact earlier tool outputs after pruning. Compaction summaries mitigate this. Test by asking about earlier conversation after a pruning event.

**Expected impact**: 20-30% reduction in context size for long sessions, which reduces both input token cost and improves response quality (less noise in context).

---

## Phase 4: Cheaper Models for Subagents

**What**: Route subagent tasks to cheaper models based on task complexity, with quality verification.

**Why**: Currently ALL subagents inherit the session model (Opus 4.6 or whatever the session is on). Most subagent tasks (council advisors, research queries, simple generation) don't need frontier-model quality. ZAI GLM-4.7 is free and handles many tasks well. Copilot Sonnet/Haiku are much cheaper quota-wise than Opus.

### Model Tier Strategy

| Tier | Model | Use Case | Cost |
|------|-------|----------|------|
| **Free** | `zai/glm-4.7` | Bulk subagent work: council advisors, brainstorming, summarization, classification | $0 |
| **Free-fast** | `zai/glm-4.7-flash` | Simple/short subagent tasks: acknowledgments, formatting, quick lookups | $0 |
| **Cheap** | `litellm/copilot-claude-haiku-4.5` | Tasks needing Claude quality but not heavy reasoning | Low quota |
| **Standard** | `litellm/copilot-claude-sonnet-4.6` | Tasks needing strong reasoning, code generation, analysis | Medium quota |
| **Frontier** | `litellm/copilot-claude-opus-4.6` | Only for: main session, referee/meta-arbiter, critical decisions | High quota |

### Implementation

#### 4a. Council Skill — Default to GLM-4.7

Update council skill to use cheaper models by default:

| Council Role | Default Model | Override for `tier=heavy` |
|-------------|---------------|--------------------------|
| Personality advisors | `zai/glm-4.7` | `litellm/copilot-claude-sonnet-4.6` |
| D/P Freethinkers | `zai/glm-4.7` | `litellm/copilot-claude-sonnet-4.6` |
| D/P Arbiters | `zai/glm-4.7` | `litellm/copilot-claude-sonnet-4.6` |
| Referee / Meta-Arbiter | `litellm/copilot-claude-sonnet-4.6` | `litellm/copilot-claude-opus-4.6` |

When spawning subagents via `sessions_spawn`, pass the `model` parameter:
```json
{
  "task": "...",
  "mode": "run",
  "label": "council-pragmatist",
  "model": "zai/glm-4.7"
}
```

#### 4b. General Subagent Routing Guidelines

Encode these in AGENTS.md or a workspace convention file so all future subagent spawns follow the pattern:

**Use `zai/glm-4.7` (free) when**:
- Task is well-defined with clear constraints
- Output format is specified in the prompt
- Task is one of: summarization, brainstorming, classification, translation, formatting, simple Q&A
- Task doesn't require tool use or complex multi-step reasoning

**Use `litellm/copilot-claude-sonnet-4.6` (standard) when**:
- Task requires nuanced reasoning or analysis
- Task involves code generation or review
- Output quality is user-facing and high-stakes
- Task requires understanding subtle context

**Use `litellm/copilot-claude-opus-4.6` (frontier) when**:
- Main interactive session only
- Final synthesis / referee / meta-arbiter roles
- Tasks where the user explicitly asked for highest quality

#### 4c. Quality Verification Strategy

Before switching council and subagents to GLM-4.7, run a quality comparison:

1. **Same-topic test**: Run the personality council on a topic we've already tested with Sonnet, but using GLM-4.7 for advisors. Compare output quality side by side.
2. **Structured output test**: Verify GLM-4.7 follows prompt templates correctly (word count guidance, section headers, role staying).
3. **Scoring rubric**:
   - Does the advisor stay in character? (yes/no)
   - Is the output substantive (not generic platitudes)? (1-5)
   - Does it follow word count guidance? (within 50% of target)
   - Does it reference specific aspects of the topic? (1-5)
4. **Minimum quality bar**: If GLM-4.7 scores ≥3.5/5 average on the rubric, it's good enough for advisor roles. Referee always stays on Sonnet+.

#### 4d. Prompt Engineering for Cheaper Models

Cheaper models need tighter prompts to maintain quality. Key techniques:

- **Be more explicit about output format**: Include examples, not just descriptions
- **Constrain output length more tightly**: "Respond in exactly 3 paragraphs" vs "200-400 words"
- **Use structured output requests**: Ask for numbered lists, specific headers
- **Front-load the most important instruction**: Put the role and constraint first, context second
- **Include a quality check instruction**: "Before responding, verify your output matches the requested format"

---

## Implementation Order

### Step 1: Config changes (Phases 1-3) — Do together, single commit

Apply all three config changes to `~/.openclaw/openclaw.json`:
- `cacheRetention: "long"` on Claude models
- `heartbeat.every: "25m"` for main, `"55m"` default
- `contextPruning.mode: "cache-ttl"` with `ttl: "1h"`

Restart gateway: `openclaw gateway restart`

Verify with `/status` and `/usage full` over next few interactions.

### Step 2: Quality test GLM-4.7 for subagent work

Run a single council advisor (e.g., Pragmatist) on a known topic using `model: "zai/glm-4.7"` in `sessions_spawn`. Compare output quality against the Sonnet run we already have saved.

### Step 3: Update council skill for model tiers

If GLM-4.7 passes quality bar, update `skills/council/SKILL.md` and `scripts/council.sh` with the model tier routing table. Update `references/prompts.md` with tighter prompt variants for cheaper models if needed.

### Step 4: Update AGENTS.md with subagent routing guidelines

Add a section documenting when to use which model tier for subagents, so the convention is followed consistently.

### Step 5: Monitor and tune

- Track cache hit rates over 1-2 days
- Monitor if context pruning causes any information loss
- Adjust heartbeat timing if cache misses are too frequent
- Tune GLM-4.7 prompts based on observed output quality

---

## What This Does NOT Change

- **No OpenClaw code changes**: Everything is config-only in `openclaw.json`
- **No upstream divergence**: All settings use documented OpenClaw config knobs
- **No new infrastructure**: No proxy servers, routers, or middleware
- **Main session stays on Opus**: Only subagents move to cheaper models
- **Fully reversible**: Remove the config keys to revert to current behavior

---

## Expected Combined Impact

| Optimization | Estimated Savings | Confidence |
|-------------|-------------------|------------|
| Prompt caching | 40-60% input token reduction | High |
| Cache warming via heartbeat | Maintains cache savings across idle | High |
| Context pruning | 20-30% context size reduction for long sessions | Medium |
| Subagent model routing | 60-80% subagent cost (free model for bulk work) | Medium (pending quality test) |

**Combined**: Significant reduction in Copilot quota burn. Main session quality unchanged. Subagent quality maintained through tighter prompts + quality verification.