Last verified: 23 September 2026 against the models overview and claude.com/pricing. Historical strings below the current table were not each re-fetched.
Model Accuracy Note — Updated May 2026
Current models (23 September 2026): Fable 5.1 · Opus 5.5 · Sonnet 5 · Haiku 4.5. Opus 5, Fable 5, Opus 4.8, and Sonnet 4.6 are legacy. Current model tracker →
Direct Answer (23 September 2026): Current Claude API IDs are claude-fable-5-1, claude-opus-5-5 (start here for most workloads), claude-sonnet-5, and claude-haiku-4-5-20251001 (alias claude-haiku-4-5). Opus 5 and claude-opus-4-8 are legacy, not the current lineup.
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 identifier desk. The current lineup below was read 23 September 2026. Older strings further down are not the current default.
claude-fable-5-1, claude-opus-5-5, claude-sonnet-5, and claude-haiku-4-5-20251001. Dateless IDs from the 4.6 generation on are pinned snapshots. Haiku 4.5 still has a dated ID plus the alias claude-haiku-4-5.
Current Claude API model strings (23 September 2026)
| Model | API Model String | Context Window | Best for |
|---|---|---|---|
| Claude Fable 5.1 | claude-fable-5-1 | 1M tokens | Demanding reasoning and long-horizon work. $10 / $50 |
| Claude Opus 5.5 | claude-opus-5-5 | 1M tokens | Daily driver. Start here for most workloads. $4 / $20 |
| Claude Sonnet 5 | claude-sonnet-5 | 1M tokens | Current Sonnet. $2 / $10 |
| Claude Haiku 4.5 | claude-haiku-4-5-20251001 | 200K tokens | Speed tier. Alias claude-haiku-4-5. $1 / $5. Max output 64K |
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.
On other platforms: Amazon Bedrock IDs for the current lineup use an anthropic. prefix: anthropic.claude-fable-5-1, anthropic.claude-opus-5-5, anthropic.claude-sonnet-5, anthropic.claude-haiku-4-5. Legacy names still on the models overview: Fable 5, Opus 5, Opus 4.8, Opus 4.7, Opus 4.6, Opus 4.5, Sonnet 4.6, Sonnet 4.5.
How to Use Model Strings in an API Call
import anthropic
client = anthropic.Anthropic()
message = client.messages.create(
model="claude-opus-5-5", # current daily driver, 23 September 2026
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:
Use Haiku (claude-haiku-4-5-20251001) when: you need speed and low cost at scale — classification, extraction, routing, metadata, high-volume pipelines where every call matters to your budget.
Use Sonnet 5 (claude-sonnet-5) when: you want the current Sonnet at $2 / $10. It is not the model docs say to start with.
Use Opus 5.5 (claude-opus-5-5) when: you are starting most workloads. Input $4 / output $20 per million tokens.
Use Fable 5.1 (claude-fable-5-1) when: evals on Opus 5.5 at higher effort still fall short. $10 / $50.
API Pricing by Model
| Model | Input (per M tokens) | Output (per M tokens) |
|---|---|---|
| Claude Haiku 4.5 | $1.00 | $5.00 |
| Claude Sonnet 5 | $2.00 | $10.00 |
| Claude Opus 5.5 | $4.00 | $20.00 |
| Claude Fable 5.1 | $10.00 | $50.00 |
| Legacy: Sonnet 4.6 | $3.00 | $15.00 |
| Legacy: Opus 5 and Opus 4.8 | $5.00 | $25.00 |
The Batch API is 50% off input and output. 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
What is the Claude API model string for Sonnet?
The current Sonnet string is claude-sonnet-5. Sonnet 4.6 (claude-sonnet-4-6) is legacy at $3 / $15.
How do I specify which Claude model to use in the API?
Pass the model string in the model parameter of your API call. For example: model="claude-sonnet-5". The model string must match exactly — Anthropic’s API will return an error if the string is invalid or deprecated.
What Claude API model should I use for production?
Start with Opus 5.5 (claude-opus-5-5) for most workloads. Use Haiku 4.5 when speed and cost are the priority. Use Fable 5.1 when Opus 5.5 at higher effort still falls short.
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