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Claude Sonnet 4.5

Anthropic · Claude 4

Balanced Claude tier for production reasoning, coding, and long-context assistant workflows.

Part of Claude Sonnet family · Other versions: Claude Sonnet 4.6
Type
multimodal
Context
200K tokens
Max Output
64K tokens
Status
current
Input
$3/1M tok
Output
$15/1M tok
API Access
Yes
License
proprietary
reasoning coding multimodal tool-use balanced
Released September 2025 · Updated March 27, 2026

Overview

Freshness note: Model capabilities, limits, and pricing can change quickly. This profile is a point-in-time snapshot last verified on March 27, 2026.

Claude Sonnet 4.5 is Anthropic’s previous default production Sonnet model. It remains relevant for teams that pinned deployments before the Sonnet 4.6 launch or want a stable historical comparison against the current default.

Capabilities

The model is effective in structured reasoning, technical writing, implementation planning, and tool-enabled assistant workflows. It is a strong fit for mixed enterprise tasks where instruction fidelity and predictable behavior matter more than frontier benchmark chasing.

Technical Details

Anthropic’s Sonnet 4.5 launch positioned it as the best coding model in the world at the time, with strong agent, coding, and computer-use behavior. In March 2026, the more important context is comparative: Sonnet 4.5 is still strong, but Sonnet 4.6 is now the current default and the model Anthropic recommends for most new Claude builds.

Pricing & Access

Current Anthropic pricing for Sonnet 4.5 remains 3per1Minputtokensand3 per 1M input tokens and 15 per 1M output tokens. Access depends on whether your stack still exposes the pinned Sonnet 4.5 alias, so teams should verify exact model availability before rollout. For new work, Sonnet 4.6 is usually the better default.

Best Use Cases

Good choice for engineering copilots, technical documentation workflows, analysis-heavy support tooling, and mid-to-high complexity product planning, especially when you need continuity with earlier Sonnet 4.5-based evals or workflows.

Comparisons

Compared with Claude Sonnet 4.6, Sonnet 4.5 is the older default with a lower current upside. Compared with Claude Opus 4.6, it is more cost-efficient but less powerful on the hardest reasoning tasks. Compared with GPT-5.4, selection often comes down to ecosystem fit and workflow preference.