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Claude Sonnet 4.5

Proprietary Anthropic · 2025-09-29 · Proprietary

September 29 2025 incremental update of the Sonnet line at the same $3 / $15 price point as Sonnet 4. Shipped alongside Claude Code checkpoints, a native VS Code extension, context editing and memory tools for long-running agents, and the Claude Agent SDK. OSWorld score of 61.4% positioned it as the strongest computer-use model from Anthropic at launch.

Cost

$3.00 / Mtok input
$15.00 / Mtok output

Anthropic API · as of 2026-05-21

source ↗

Speed

48.8 tok/sec output
1441 ms TTFT

· as of 2026-05-21

source ↗

Architecture

tokens in Embedding vocab not disclosed × N layers Architecture not disclosed (proprietary or undocumented) Output projection tokens out
Schema-generated from data/models.yaml. Every label is auditable against the model's sources.

Specs

Architecture
unknown
Total params
not disclosed
Active params
not disclosed
Context window
not verified
Attention
unknown
Position encoding
unknown
Post-training
rlhf, constitutional
OSI-approved
no
Data released
no
Training code
not released

Benchmarks

Each score carries the date it was published; we never infer or interpolate missing scores.

General reasoning

MMLU-Pro 86.0 as of 2026-05-21 source ↗
GPQA-Diamond 72.7 as of 2026-05-21 source ↗

Code

SWE-Bench Verified 77.2 as of 2025-09-29 source ↗
LiveCodeBench 59.0 as of 2026-05-21 source ↗

Math

AIME 2025 37.0 as of 2026-05-21 source ↗

Available quantizations

None. The weights are not distributed, so there are no public quantizations.

Notable innovations

  • · Claude Code checkpoints (progress save / rollback)
  • · Claude Agent SDK
  • · Context editing and memory tools for long-running agents
  • · Native VS Code extension

Lineage

Incremental Sonnet update; the agent-coding tooling around the model is the headline change.

Derived from

Claude Sonnet 4 2025-05-22

Sources