Claude Model Names: Every Anthropic API Model ID and Alias

You copied a model string from an old tutorial, sent a request, and got an error back. Or you're wiring up a new app and can't tell whether claude-sonnet-5-5 and "Claude Sonnet 5.5" are the same thing. This page is the lookup table for Anthropic API model names: every current Claude model ID, what the aliases do, which IDs are retired, and which model Claude Code uses by default.

Here's the short version, as of October 2026, from Anthropic's models overview:

Paste the string in the right-hand column into the model field of your request. That's the whole job for most people. The rest of this page explains why the IDs look the way they do, what changed with the 4.6 generation, and how to stop an old ID from breaking your app.

This is a reference, not a buying guide. If you're deciding which model to run, read which Claude model is best for coding or the Claude Haiku vs Sonnet comparison instead.

Anthropic API model names, October 2026

The models overview compares four current models, one from each main line. Each has one job:

• Fable is the top tier. Anthropic describes it as "for demanding reasoning and long-horizon agentic work."
• Opus is the default recommendation. The overview page tells you to start with Opus 5.5 "for most workloads."
• Sonnet is the middle. Anthropic calls it "the best combination of speed and intelligence."
• Haiku is the fastest, built for high-volume work like classification, extraction and routing.

Here's the full current lineup with the specs that matter when you pick an ID:

On Google Cloud (both the Google-managed and Anthropic-managed versions), Microsoft Foundry, and Claude Platform on AWS, the ID is the same as the Claude API ID. Bedrock is the only platform that adds a prefix.

Prices change more often than names, so they aren't in this table. Anthropic's pricing page has the current per-token rates for each model.

What "Sonnet" means as an LLM name

People search "sonnet llm" because the name gives nothing away. Sonnet isn't a separate product. It's the mid-tier line within the Claude family, sitting between Haiku (cheaper, faster) and Opus (more capable, slower). Every Sonnet release keeps the family name and bumps the version number: Sonnet 4.6, Sonnet 5, Sonnet 5.5.

The same pattern holds for every line. "Claude Opus 5.5" is the display name. claude-opus-5-5 is the API model ID. They point at the same model.

Mythos models in the deprecations table

Anthropic's deprecations table also lists claude-mythos-5-1 and claude-mythos-5 as active, but neither appears in the main comparison on the overview page. If you don't already know you have access to them, use the four IDs above.

How Claude model IDs work

Two naming schemes are in use, and the split falls at the 4.6 generation. Anthropic's model IDs and versioning page lays them out.

The 4.6 generation and later: dateless IDs

From Claude Opus 4.6 and Sonnet 4.6 on, IDs follow this pattern:

claude-{name}-{major}[-{minor}]

Major releases drop the minor number. That's why you see claude-sonnet-5 and claude-opus-5, but claude-opus-5-5 and claude-opus-4-8.

The important part: a dateless ID is not an evergreen pointer. Anthropic's docs call this "a common misconception." claude-sonnet-4-6 maps to one fixed snapshot. Anthropic doesn't change the weights behind an existing ID. When a better version ships, it gets a new ID.

Before the 4.6 generation: dated IDs and aliases

Older models carry a snapshot date in the ID:

claude-{name}-{major}-{minor}-{YYYYMMDD}

So Claude Sonnet 4.5 is claude-sonnet-4-5-20250929, and Claude Haiku 4.5 is claude-haiku-4-5-20251001.

For these older models, the Claude API also accepts a shorter alias, such as claude-sonnet-4-5. That alias is a pointer: it resolves to the most recent dated snapshot for that minor version. Anthropic's stability guarantee covers the model ID, not the alias.

On the current models, there's nothing to resolve. The overview table lists the "alias" for Opus 5.5 as claude-opus-5-5, the same string as the ID, because the dateless ID is already the pinned snapshot.

Platform formats for older models

The cloud platforms format dated IDs differently, which is where most copy-paste errors come from:

Bedrock dropped the -v1 suffix starting with Sonnet 4.6. Opus 4.6 is the last Bedrock ID that has it: anthropic.claude-opus-4-6-v1.

Same ID, slightly different behavior

The weights behind an ID never change, but the serving infrastructure around them can. Anthropic's docs name the request router, safety classifiers and sampling logic. If a stable ID suddenly behaves a little differently, Anthropic says an infrastructure update is the most likely cause, not a model swap.

Legacy and retired Claude model IDs

Anthropic keeps older models callable for a while after a new release. Here's where each one stood as of October 2026, per the model deprecations page:

"Legacy" means the model won't get updates and could be deprecated later. "Deprecated" means it still works but has a retirement date. Retired models fail every request.

Two things to act on now:

• Sonnet 4.5 retires November 30, 2026. Anthropic's recommended replacement is claude-sonnet-5-5.
• Every Claude 3.x ID is retired. If your code still says claude-3-5-sonnet-20241022 or claude-3-opus-20240229, it's already failing. Note the old naming order too: Claude 3 IDs put the version before the name (claude-3-5-sonnet), while Claude 4 and later put the name first (claude-sonnet-4-5).

These dates apply to Anthropic-operated platforms. Amazon Bedrock and Google's managed version of Claude set their own schedules, so check their model tables if you call Claude there.

Which model does Claude Code use?

Claude Code doesn't ask you to type an ID. When you leave the model on default, it resolves to a model based on how you sign in. According to the Claude Code model configuration docs as of October 2026:

Claude Code also has its own short aliases, separate from the API's. On the Anthropic API, opus, sonnet and haiku resolve to Opus 5.5, Sonnet 5.5 and Haiku 5.5. best uses Fable where you have access to it and Opus otherwise.

These aliases move when Anthropic ships a new model. To pin a version in Claude Code, use the full model ID, for example claude-opus-5-5. The docs also list minimum versions: Opus 5.5 needs Claude Code v2.1.280 or later, Sonnet 5.5 needs v2.1.284, and the docs say to use v2.1.293 or later with Haiku 5.5.

Switching models, setting a default in settings.json, and the precedence between all of them is a topic of its own. The Claude Code default model guide walks through every method.

How to get the model list from the API

Tables like the ones above go stale. The API can tell you what your key can call right now. The List Models endpoint is GET /v1/models, and Anthropic's own example request looks like this:

curl https://api.anthropic.com/v1/models \
    -H 'anthropic-version: 2026-10-21' \
    -H "Authorization: Bearer $ANTHROPIC_API_KEY"

Each model in the response includes:

• id: the string to send as model, such as claude-opus-5-5
• display_name: the human name, such as "Claude Opus 5.5"
• lifecycle: active, deprecated or retired
• retires_at: the scheduled retirement date, if one is set
• max_input_tokens and max_tokens: the context window and output limit
• line: haiku, sonnet, opus, fable or mythos

By default the list includes active and deprecated models. Retired ones only show up if you ask for them with the lifecycle filter. Anthropic says to read line rather than parse it out of the ID, since more lines may be added. That's useful if you're building a model picker. The context window numbers per model also differ between the API and the Claude apps, which the Claude context window guide covers.

How to choose and pin a model ID

A few habits keep model names from breaking things:

1. Store the ID in config, not in code. One environment variable means one change when you upgrade.
2. Send the full ID in production. On current models the dateless ID is already pinned. On pre-4.6 models, use the dated ID rather than the alias, since the alias can move.
3. Watch the deprecations page. Anthropic says it gives at least 60 days' notice before retiring a publicly released model, and emails customers with active deployments.
4. Audit before a retirement date. Anthropic's suggested check: go to the Usage page in Claude Console, click Export, and look for old model names in the CSV.
5. Test the replacement first. A new ID is a new model. Anthropic publishes migration guides because prompts don't always carry over unchanged.

FAQ

What are the current Anthropic API model names?

As of October 2026: claude-fable-5-1, claude-opus-5-5, claude-sonnet-5-5 and claude-haiku-5-5. Anthropic's models overview page has the current list.

What is the difference between a Claude model ID and an alias?

From the 4.6 generation on, there's no practical difference: the dateless ID is the pinned snapshot. For older models, the alias (like claude-sonnet-4-5) points to the latest dated snapshot, while the dated ID (like claude-sonnet-4-5-20250929) never changes.

Which model does Claude Code use?

On Pro, Max, Team, Enterprise and the Anthropic API, the default is Opus 5.5 as of October 2026. Microsoft Foundry defaults to Sonnet 4.5.

Is claude-sonnet-4-6 always the latest Sonnet?

No. It always points to Sonnet 4.6. The newest Sonnet ships under its own ID, which is claude-sonnet-5-5 as of October 2026.

Why does my old Claude model ID return an error?

The model is probably retired. All Claude 3.x models, Claude Sonnet 4 and Opus 4, and Opus 4.1 are retired on the Claude API. Switch to a current ID from the table above.

Are model names the same on Amazon Bedrock?

Not quite. Bedrock adds an anthropic. prefix, such as anthropic.claude-opus-5-5, and older dated models also end in -v1:0.

Key points

• Four current IDs, as of October 2026: claude-fable-5-1, claude-opus-5-5, claude-sonnet-5-5, claude-haiku-5-5.
• From the 4.6 generation on, dateless IDs are fixed snapshots, not "latest" pointers.
• Older models use dated IDs. Their short aliases can move.
• Sonnet 4.5 retires November 30, 2026, and every Claude 3.x ID is already gone.
• Claude Code's default is Opus 5.5 on most plans. Its opus/sonnet/haiku aliases are separate from API IDs.
• GET /v1/models is the live source of truth for your key.

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