Anthropic's Different Philosophy
Anthropic was founded by former OpenAI researchers who believed AI safety needed to be baked into the model architecture, not bolted on afterward. This philosophical difference manifests in every technical decision behind Claude Sonnet 4.
Constitutional AI: Training With Principles
Instead of relying entirely on human feedback (which is expensive, inconsistent, and potentially biased), Anthropic developed Constitutional AI (CAI). The process works in two phases.
First, supervised learning from AI feedback (SLAIF): Claude is given a constitution — a set of principles like "be helpful, harmless, and honest" — and asked to critique and revise its own outputs according to these principles. Second, reinforcement learning from AI feedback (RLAIF): instead of humans ranking outputs, an AI trained on the constitution provides preference labels. This enables scaling alignment research without proportionally scaling human labor.
The 200K Token Context Window
Claude Sonnet 4 supports 200,000 token context windows — roughly 150,000 words or 500 pages. This isn't just a larger version of GPT's context; Anthropic's attention implementation handles long contexts more gracefully. In practice, Claude maintains coherent reasoning over very long documents with less "lost in the middle" degradation than competing models.
Extended Thinking: Chain-of-Thought at Scale
Extended thinking mode gives Claude a scratchpad to reason before responding. The model produces internal chain-of-thought tokens that aren't shown to the user but influence the final answer. On complex reasoning tasks — math proofs, legal analysis, architectural decisions — extended thinking mode improves accuracy by 15-40% in Anthropic's benchmarks.
The mechanism: the model is trained to use think tokens effectively through reinforcement learning on reasoning tasks. The scratchpad tokens are masked from the user but contribute to the final hidden state that generates the response.
Why Claude Writes Differently
Claude's outputs feel more carefully reasoned and less fluent than GPT-4o's in blind tests. This is intentional — the constitutional training biases Claude toward epistemic honesty over confident-sounding output. It will say "I'm not certain" more often than GPT, which feels less polished but is more accurate about its own limitations.
Claude vs GPT-4o: When to Use Which
Use Claude for: complex reasoning tasks, long document analysis, code review requiring architectural judgment, and any task where you want the model to push back on bad premises. Use GPT-4o for: creative writing, rapid prototyping, integration with OpenAI's ecosystem, and tasks requiring image generation in the same workflow.
Pricing and Access
Claude Sonnet 4 via API: $3/million input tokens, $15/million output tokens. Claude Pro subscription: $20/month for 5x usage vs free. For most professional use cases, Claude via API with smart caching is more cost-effective than the subscription. See Claude in our catalog →