Current as of March 2026. Opus 4.5 sits at $5/$25 input/output — same price as Opus 4.6 but without the million-token context window. That makes it a harder sell now that 4.6 exists. Still, if you need Opus-tier reasoning and 200K context is enough, it’s a legitimate choice.
Specs
| Provider | Anthropic |
| Input cost | $5.00 / M tokens |
| Output cost | $25 / M tokens |
| Context window | 200K tokens |
| Max output | 64K tokens |
| Parameters | N/A |
| Features | function_calling, vision, reasoning |
What it’s good at
Reliable Function Calling
It follows tool schemas more precisely than Sonnet. When your agent’s execution loop keeps breaking on hallucinated arguments, stepping up to Opus-tier often fixes it without needing to debug your prompt.
64K Output Buffer
Same 64K ceiling as Sonnet 4.5, so you get full code modules in a single response. Useful when you know you need the output space and the reasoning depth.
Where it falls short
High Latency
Noticeably slower than the 3.5 series. Not a dealbreaker for background tasks, but interactive workflows feel sluggish.
Premium Pricing
$25/M output is hard to justify unless you’re genuinely hitting a reasoning ceiling on Sonnet. If the task isn’t breaking on logic, you’re overpaying.
Best use cases with OpenClaw
- Complex Repository Refactoring — Cross-file dependency reasoning is where Opus earns its price. Sonnet misses things here; Opus usually doesn’t.
- Autonomous Research Agents — Long execution traces with many tool calls benefit from the better instruction following. Less babysitting.
Not ideal for
- Simple Data Extraction — Sonnet or Haiku handle basic JSON extraction just fine for a third of the cost. Opus is overkill.
- Real-time Chat Interfaces — Time-to-first-token is too high. Users waiting on a support bot response will notice the lag.
Run it through Haimaker
Skip juggling API keys. One Haimaker key gives you access to every model on the platform. Tell OpenClaw:
Add Haimaker as a custom provider to my OpenClaw config. Use these details:
- Provider name: haimaker
- Base URL: https://api.haimaker.ai/v1
- API key: [PASTE YOUR HAIMAKER API KEY HERE]
- API type: openai-completions
Add the auto-router model:
- haimaker/auto (reasoning: false, context: 128000, max tokens: 32000)
Create an alias "auto" for easy switching. Apply the config when done.
Or skip model selection entirely — Haimaker’s auto-router picks the best model for each task so you don’t have to.
OpenClaw setup
Set your API key and OpenClaw handles the rest.
export ANTHROPIC_API_KEY="your-key-here"
That’s it. OpenClaw picks up Anthropic models automatically.
How it compares
- vs GPT-4o — Opus 4.5 follows complex system prompts more consistently. GPT-4o is faster and cheaper for input-heavy tasks where reasoning depth isn’t the issue.
- vs Claude 3.5 Sonnet — Sonnet is the right daily driver for most coding tasks. Reach for Opus 4.5 only when reasoning is the actual bottleneck, not when you’re just hoping a bigger model fixes a vague problem.
Bottom line
The ‘big brain’ model you call when Sonnet keeps failing on the same task. Expensive and slow — that’s the tradeoff. Worth it when the logic is genuinely hard; not worth it when the problem is actually in your prompt.
TRY CLAUDE OPUS 4.5 ON HAIMAKER
For setup instructions, see our API key guide. For all available models, see the complete models guide.