claude-opus-4

claude-opus-4

by Anthropic
3.0
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Pros & Cons

Pros

  • Strong Long-Horizon Reasoning: Could maintain focused effort across thousands of steps, useful for complex multi-stage legal workflows.
  • Memory Across Long Tasks: Supported "memory files" to retain key facts over extended work, improving continuity on large document reviews.
  • Large Context and Output: A 200K-token context window with up to 64K output tokens supported processing sizable legal document sets.

Cons

  • Fully Retired: Anthropic retired Claude Opus 4 on June 15, 2026; API calls now fail with no automatic failover, making it unusable for current workflows.
  • No Legal-Specific Training: Not trained on specialized legal datasets or case-law databases, so it lacked jurisdiction-specific legal reasoning and citation grounding.
  • Higher-Risk Classification and Cost: Anthropic classified it as a higher-risk "Level 3" model requiring enhanced safeguards, and as the flagship model it was priced at a premium versus Sonnet-tier models.

About claude-opus-4

Introduction

Claude Opus 4 was Anthropic's flagship model, released May 22, 2025 alongside Claude Sonnet 4, built for the most demanding reasoning, coding, and long-horizon agentic tasks. It offered hybrid near-instant and extended-thinking modes, could maintain focused effort across thousands of steps in a workflow, supported "memory files" to retain key facts across long tasks when given local file access, and shipped with a 200K context window and up to 64K output tokens. Anthropic classified it as a higher-risk "Level 3" model requiring enhanced safety measures. Like other general-purpose models, it was not trained on specialized legal datasets or case-law databases, so it lacked deep jurisdiction-specific legal reasoning despite its advanced general reasoning ability.

2026 Status: Retired

Anthropic retired Claude Opus 4 on June 15, 2026, in the same deprecation wave as Claude Sonnet 4, following an April 2026 notice. API calls to the claude-opus-4 model ID now fail with no automatic failover. Anthropic's recommended successors are Claude Opus 4.6 and Claude Opus 4.8 for complex or agentic workloads (Claude Sonnet 4.5/4.6 are lighter-weight alternatives). Any legal tooling still referencing this model ID needs an explicit migration.

Use in Legal Work

While available, Opus 4's long-horizon reasoning and memory features made it one of the stronger general-purpose options for complex, multi-step legal workflows — for example, working through a large document set while retaining context across steps. It never had native legal-database access, built-in citation verification, or legal-specific fine-tuning, so legal use always required professional review, and its retirement now rules it out for any current or new legal-AI workflow.

Frequently Asked Questions

No. Anthropic retired it on June 15, 2026 in the same wave as Claude Sonnet 4, and API calls to the claude-opus-4 model ID now fail with no automatic failover. Recommended successors are Claude Opus 4.6/4.8 for complex work, or Claude Sonnet 4.5/4.6 for lighter workloads.

Yes, relative to other general-purpose models at the time: its long-horizon reasoning and memory-file support helped it stay coherent across long, multi-step reviews. It still had no legal-database grounding or citation verification, so outputs required review by a qualified legal professional.

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