Claude API Model Strings, IDs and Specs — Complete Reference (April 2026)

When you’re building on Claude via the API, you need the exact model string — not just the name. Anthropic uses specific model identifiers that change with each version, and using a deprecated string will break your application. This is the complete reference for Claude API model names, IDs, and specs as of April 2026.

Current Claude API Model Strings (April 2026)

Anthropic publishes the full, current list of model strings in their official models documentation. Always verify there before updating production systems — model strings are updated with each new release.

How to Use Model Strings in an API Call

import anthropic

client = anthropic.Anthropic()

message = client.messages.create(
    model="claude-sonnet-4-6",  # ← model string goes here
    max_tokens=1024,
    messages=[
        {"role": "user", "content": "Your prompt here"}
    ]
)

print(message.content)

Model Selection: Which String to Use When

The right model depends on your task requirements. Here’s the practical routing logic:

API Pricing by Model

The Batch API offers roughly 50% off all rates for asynchronous workloads. For a full pricing breakdown, see Anthropic API Pricing: Every Model and Mode Explained.

Important: Versioned Strings vs. Aliases

Anthropic occasionally provides alias strings (like claude-sonnet-latest) that point to the current version of a model family. These are convenient for development but can create problems in production — when Anthropic updates the model the alias points to, your application silently starts using a different model without a code change. For production systems, always pin to a versioned model string and upgrade intentionally.

Frequently Asked Questions