Claude 4.5

TL;DR

• Claude 4.5 is Anthropic's 2025 flagship model. Current main SKUs: Sonnet 4.5 (primary) and Haiku 4.5 (lightweight/low-cost).
• Good at: long document/table comprehension (200K default, optional 1M beta), structured output (JSON/tables), writing analysis, and stable code/tool calling.
• Model selection advice: start with Haiku 4.5 to get things working, then upgrade to Sonnet 4.5 for quality. Use 10-50 samples for eval -- check accuracy, format stability, and hallucination rate.

Key Focus Areas

When reading this page, pay attention to:

1. Context window (200K default, enterprise can request 1M beta)
2. Structured output capabilities (JSON/Tool Calling stability)
3. Hallucination and factual question answering performance
4. Code/table comprehension: improvements over Claude 3.5

For production use, lock down the output format (schema) and add self-check (e.g., require evidence/quoted snippets).

What's New (4.5 vs 3.x/3.5)

• Long context: 200K default; enterprise/specific endpoints can use 1M beta (requires dedicated Header).
• More stable structured output: JSON/schema constraints drop fewer fields, function calling is more robust in loops/error recovery.
• Code and tables: Better code comprehension/generation, more stable table/CSV extraction.
• Safety and alignment: Fewer refusals, but still recommended to output "source/confidence" for auditing.

Usage Tips

• Prompt structure: System message defines role/format/constraints, User provides context + task, add self-check when needed.
• JSON/tool calling: Temperature 0-0.3; require the model to self-check field completeness before output; limit tool calling rounds to avoid loops.
• Long documents: Summarize in sections then consolidate; for traceability, have the model output "quoted snippet + paragraph number."
• Latency/cost: Haiku 4.5 for high concurrency; Sonnet 4.5 for critical quality steps.

References (Official)

• Claude 4.5 Launch
• Model Card (Claude 4.5 Sonnet/Haiku)
• Context window & beta headers