What it is
Anthropic's Claude API is the LLM we default to in our test rig and recommend by name in most agent comparison guides.
Why we use it
- Most reliable tool-use behaviour we've measured
- Long context (1M tokens) makes complex agent tasks tractable
- Prompt caching cuts costs 50-90% on stable system prompts
- Anthropic's safety posture is unusually strong vs competitors
Why we wouldn't
- Pricing premium vs OpenRouter for the same model
- Rate limits can bite at sustained agent throughput
Best for
- Agentic workloads where quality matters
- Long-context tasks (codebases, document analysis)
- Production deployments with tight latency requirements
Not for
- Cost-optimisation as primary goal (use OpenRouter)
- Fully offline workloads (use ZeroClaw + local model)
Long review
Claude 4.5 Sonnet is the most reliable agentic model we tested in 2026. Tool-use behaviour is consistently better than GPT-5 in our blind tests; the model rarely hallucinates tool names, rarely calls non-existent functions, rarely misformats arguments. Long context (1M tokens) is genuinely usable, not just nominal — long-context retrieval quality is the highest in the market. Prompt caching cuts production costs dramatically. Pricing premium vs raw cost-optimisation gateways like OpenRouter is meaningful but justifiable for the quality. The Anthropic team's commitment to AI safety, while sometimes inconvenient at the API level, has shipped very few embarrassing failures. We pay for Claude usage out of our own budget for testing — and we recommend it to anyone whose budget supports it.
Alternatives we've tested
- OpenAI (GPT API) — GPT-5 is competitive with Claude on many tasks. The API is the most mature in the market; the agent behaviour is more variable.
- OpenRouter — LLM gateway with unified API across 100+ providers. Our default for cost-optimisation and provider fallback.