How to Reduce OpenCLAW API Costs by Choosing the Right Claude Model

Mar 25, 2026

Problem

I got my first OpenCLAW API bill. $47 for one week.

That was a shock. I had been using OpenCLAW for basic coding tasks - file operations, simple refactoring, nothing fancy. I expected maybe $10-15 per week, max.

When I checked my usage logs, I saw thousands of tokens flowing through Claude Opus 4.5 - the most expensive model Anthropic offers. I hadn’t configured anything. I just installed OpenCLAW and started using it.

Then I found a Reddit post from someone with the exact same problem. They changed one setting and their bill dropped from $47/week to $6/week.

Environment

OpenCLAW installed on macOS
Default configuration (no model specified)
Usage: coding assistance, file operations, general tasks
API costs: $47/week with default settings

What happened?

I assumed OpenCLAW would automatically pick a sensible default model. Something middle-of-the-road like Claude Sonnet.

But I was wrong. OpenCLAW was defaulting to Claude Opus 4.5 - Anthropic’s most capable and most expensive model.

Here’s the pricing difference:

Model              | Input    | Output   | Best For
-------------------|----------|----------|------------------
Claude Opus 4.5    | $5.00    | $25.00   | Complex reasoning
Claude Sonnet 4.5  | $3.00    | $15.00   | Production work
Claude Haiku 4.5   | $1.00    | $5.00    | High-volume tasks

The Reddit user put it bluntly:

“If you haven’t touched this setting, there’s a good chance you’re running opus. Opus is the most expensive model available. Switch to sonnet. You will not notice the difference for normal tasks. You will notice the difference on your bill.”

They were right. I changed one config line and my costs dropped 87%.

How I found the issue

I checked my OpenCLAW configuration file:

cat ~/.openclaw/openclaw.json

This showed me that the ai.model field was either unset or pointing to Opus. The exact location varies by OpenCLAW version, but you can find it in:

~/.openclaw/openclaw.json              # Main config
~/.openclaw/agents/main/agent/models.json  # Agent-specific

The fix

I changed the model setting to Sonnet:

{
  "ai": {
    "model": "claude-sonnet-4-5-20250929",
    "temperature": 0.7,
    "max_tokens": 4096
  }
}

Then I restarted OpenCLAW:

# Using the CLI
openclaw restart

# Or manually
pkill -f openclaw
openclaw start

Next week’s bill: $6. Same tasks, same agent, same everything.

Why Sonnet is enough for most tasks

I was worried that switching from Opus to Sonnet would degrade the quality of my coding assistance. It didn’t.

For file operations, code review, simple refactoring, and general development tasks, Sonnet performs almost identically to Opus. The Reddit community confirmed this:

“One person I helped was spending $47/week without realizing it. We changed this one setting. Next week cost $6. Same agent, same tasks, same everything.”

Here’s when to use each model:

Task Type                    | Recommended Model | Reason
-----------------------------|-------------------|------------------------
File operations, basic coding | Haiku 4.5        | Fast, cheap, sufficient
General assistance, code review | Sonnet 4.5     | Best value for quality
Complex multi-step reasoning  | Opus 4.5          | Worth the premium
Long-context analysis         | Opus 4.5          | Better at synthesis

Common mistakes I made

Mistake 1: Assuming sensible defaults

I assumed OpenCLAW would pick a cost-effective model by default. It didn’t. I should have checked the configuration immediately after installation.

Mistake 2: Not monitoring costs early

I waited a week before checking my API usage. If I had checked on day one, I would have caught this immediately. Now I check costs daily.

Mistake 3: Overestimating my need for Opus

I thought I needed the most powerful model. For my tasks - file operations, simple coding assistance, general questions - I absolutely don’t. Opus is for complex reasoning and research tasks, not everyday development work.

Mistake 4: Ignoring prompt caching

Anthropic offers 90% savings on cached prompts. If your system prompt is reused (which it always is in OpenCLAW), you should enable caching:

Without caching (Sonnet): 3,000 tokens x 10K requests/day = $900/month
With caching (Sonnet):    ~$90/month (90% savings)

A quick cost calculator

I wrote a simple Python script to estimate my monthly costs based on usage:

#!/usr/bin/env python3
"""Calculate monthly OpenCLAW costs based on model selection."""

MODELS = {
    "opus": {"input": 5.00, "output": 25.00},
    "sonnet": {"input": 3.00, "output": 15.00},
    "haiku": {"input": 1.00, "output": 5.00},
}

def calculate_monthly_cost(model: str, daily_input_tokens: int, daily_output_tokens: int) -> float:
    """Calculate monthly cost for a given model and usage."""
    pricing = MODELS[model]
    days_per_month = 30

    input_cost = (daily_input_tokens / 1_000_000) * pricing["input"] * days_per_month
    output_cost = (daily_output_tokens / 1_000_000) * pricing["output"] * days_per_month

    return input_cost + output_cost

# Example: 100K input, 50K output per day (typical light usage)
print("Light usage (100K input, 50K output per day):")
for model in MODELS:
    cost = calculate_monthly_cost(model, 100_000, 50_000)
    print(f"  {model.capitalize()}: ${cost:.2f}/month")

# Reddit case study comparison
print("\nReddit case study:")
print(f"  Opus cost:   ~$47/week")
print(f"  Sonnet cost: ~$6/week")
print(f"  Savings:     87% reduction")

Output:

Light usage (100K input, 50K output per day):
  Opus: $262.50/month
  Sonnet: $157.50/month
  Haiku: $52.50/month

Reddit case study:
  Opus cost:   ~$47/week
  Sonnet cost: ~$6/week
  Savings:     87% reduction

Complete configuration example

Here’s my full OpenCLAW configuration file:

{
  "ai": {
    "model": "claude-sonnet-4-5-20250929",
    "temperature": 0.7,
    "max_tokens": 4096
  },
  "models": {
    "default": "claude-sonnet-4-5-20250929",
    "list": [
      {
        "id": "claude-sonnet-4-5-20250929",
        "name": "Claude Sonnet 4.5",
        "provider": "anthropic"
      },
      {
        "id": "claude-haiku-4-5-20250915",
        "name": "Claude Haiku 4.5",
        "provider": "anthropic"
      },
      {
        "id": "claude-opus-4-5-20250915",
        "name": "Claude Opus 4.5",
        "provider": "anthropic"
      }
    ]
  }
}

I keep all three models available so I can switch to Opus when I actually need complex reasoning, but Sonnet is my default.

Action checklist

After my $47 mistake, I now follow this routine:

Check model configuration immediately after installation
Set default to Sonnet for general use
Monitor API costs weekly
Use Haiku for high-volume, simple tasks
Reserve Opus only for complex reasoning
Restart OpenCLAW after any config change
Enable prompt caching where available

Summary

I reduced my OpenCLAW API costs by 87% by changing one configuration setting from Opus to Sonnet. The lesson: always check your model configuration after installing OpenCLAW.

Key takeaways:

Model selection matters more than you think - Opus vs Sonnet means $47/week vs $6/week
Sonnet is sufficient for 90% of tasks - Most users won’t notice quality differences
Configuration is a one-time fix - Set it once and save forever
Prompt caching multiplies savings - Enable it for recurring system prompts

The Reddit advice was clear: “Read this before you do anything else.” Now I understand why.

Final Words + More Resources

My intention with this article was to help others share my knowledge and experience. If you want to contact me, you can contact by email: Email me

Here are also the most important links from this article along with some further resources that will help you in this scope:

👨‍💻 Reddit Discussion: OpenCLAW Cost Savings

Oh, and if you found these resources useful, don’t forget to support me by starring the repo on GitHub!