Current as of March 2026. Sonnet 4.5 is the version to pick if you’re still running 3.5 Sonnet and keep hitting the 8K output ceiling. The jump to 64K output is genuinely useful — you stop babysitting truncated responses. The reasoning improvements are real but incremental; the output limit is the actual upgrade.
Specs
| Provider | Anthropic |
| Input cost | $3.00 / M tokens |
| Output cost | $15 / M tokens |
| Context window | 200K tokens |
| Max output | 64K tokens |
| Parameters | N/A |
| Features | function_calling, vision, reasoning |
What it’s good at
Tool Calling
It follows tool schemas cleanly in OpenClaw. JSON tags close, arguments match the schema, the loop doesn’t break unexpectedly. It’s not flashy, but it’s the thing that matters most for agents.
64K Output Limit
The main reason to upgrade from 3.5 Sonnet. Full file rewrites, large refactors, long-form docs — all in one shot.
Instruction Adherence
It respects negative constraints better than GPT-4o. If your system prompt says “do not modify files outside this directory,” Sonnet 4.5 tends to actually listen.
Where it falls short
Higher Latency
Slower than 3.5 Sonnet and significantly slower than GPT-4o-mini. The reasoning improvement costs you time.
Premium Pricing
Five times the output cost of older 3.5 Sonnet. That math catches people off guard when they move from prototyping to production volumes.
Best use cases with OpenClaw
- Autonomous Coding Agents — 200K context in, 64K output out. You can read a large codebase and write a full implementation without the model losing track of what it was doing.
- Complex Data Extraction — Vision plus reasoning works well for parsing messy documents into structured JSON. Not a gimmick; I use it for this regularly.
Not ideal for
- Simple Chatbots — $3/$15 is real money for basic Q&A. Haiku handles conversational tasks at a fraction of the cost.
- Real-time UI Interactions — Time-to-first-token is too high. Anything where a user is watching a cursor blink will feel slow.
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. That’s the whole setup.
export ANTHROPIC_API_KEY="your-key-here"
That’s it. OpenClaw picks up Anthropic models automatically.
How it compares
- vs GPT-4o — More reliable for coding tasks, stricter instruction following. GPT-4o is faster and competitive on cost depending on your output volume.
- vs Claude 3.5 Sonnet — If you’re not hitting the 8K output limit on 3.5, there’s no rush to upgrade. When you do start hitting it regularly, 4.5 is the obvious next step.
Bottom line
A solid upgrade from 3.5 Sonnet specifically if output length is your bottleneck. Not a revolution — the reasoning is incrementally better, not categorically different. If you’re happy with 3.5 Sonnet’s outputs and just need more of them, this is your model.
TRY CLAUDE SONNET 4.5 ON HAIMAKER
For setup instructions, see our API key guide. For all available models, see the complete models guide.