The Claude Model Glossary is a collection of every model in 📝Anthropic's 📝Claude family, from Claude 1 in March 2023 to Claude Sonnet 5.5 in September 2026, grouped by tier and listed newest first. As of September 28, 2026, Anthropic recommends Claude Opus 5.5 for most work and Claude Fable 5.1 for the most demanding reasoning.

Glossary

Mythos Class

📝Claude Mythos — Anthropic's model tier above Opus, whose public releases ship as paired Fable and Mythos configurations of one model.
Claude Fable 5.1 — claude-fable-5-1, released September 1, 2026: the generally available Mythos-class model, stronger than Fable 5 at long-horizon agentic work, with cache reads 75% cheaper.
Claude Mythos 5.1 — claude-mythos-5-1, released September 1, 2026: the same model as Fable 5.1 with relaxed cybersecurity and life-science safeguards, offered only to vetted organizations.
📝Claude Fable 5 — claude-fable-5, released June 9, 2026: the first public Mythos-class model, which hands high-risk cybersecurity, biology, and distillation requests to Claude Opus 4.8.
📝Claude Mythos 5 — claude-mythos-5, released June 9, 2026: the less-restricted twin of Fable 5, reserved for trusted cyber-defense partners.
Claude Mythos Preview — claude-mythos-preview, April 2026: the restricted research model behind 📝Project Glasswing that surfaced thousands of zero-day vulnerabilities, deprecated June 9, 2026.

Opus

📝Claude Opus — Anthropic's high-capability tier, the most capable Claude line from March 2024 until the Mythos tier arrived above it in 2026.
📝Claude Opus 5.5 — claude-opus-5-5, released September 22, 2026: the first Claude 5.5 model, which Anthropic reports matches Fable 5.1 on most work at $4 / $20 per million tokens.
Claude Opus 5 — claude-opus-5, released July 24, 2026: the first Opus of the Claude 5 generation and a fallback model for requests that Fable 5.1 and Opus 5.5 decline.
Claude Opus 4.8 — claude-opus-4-8, released May 28, 2026: the final Claude 4 Opus and the fallback model for cybersecurity requests that Mythos-class safeguards decline.
Claude Opus 4.7 — claude-opus-4-7, released April 16, 2026: introduced the current Claude tokenizer and ended support for non-default temperature, top_p, and top_k.
Claude Opus 4.6 — claude-opus-4-6, released February 5, 2026: began Anthropic's dateless model-ID convention and the move from manual extended thinking to adaptive thinking.
Claude Opus 4.5 — claude-opus-4-5-20251101, released November 24, 2025: cut Opus pricing to $5 / $25 per million tokens, one third of the previous Opus rate.
Claude Opus 4.1 — claude-opus-4-1-20250805, released August 5, 2025: an agentic-coding upgrade to Opus 4, retired August 5, 2026.
Claude Opus 4 — claude-opus-4-20250514, released May 22, 2025: the first Anthropic model deployed under AI Safety Level 3 protections, retired June 15, 2026.
Claude 3 Opus — claude-3-opus-20240229, released March 4, 2024: the flagship of the first three-tier Claude family, retired January 5, 2026.

Sonnet

📝Claude Sonnet — Anthropic's balanced mid-tier line, positioned as the best combination of speed, intelligence, and cost.
Claude Sonnet 5.5 — claude-sonnet-5-5, released September 28, 2026: Anthropic's balance of speed and intelligence, with a 1M-token context window at $2 / $10 per million tokens.
Claude Sonnet 5 — claude-sonnet-5, released June 30, 2026: the first Sonnet of the Claude 5 generation.
Claude Sonnet 4.6 — claude-sonnet-4-6, released February 17, 2026: the replacement Anthropic designates for every retired Sonnet 3.x and Sonnet 4 model.
Claude Sonnet 4.5 — claude-sonnet-4-5-20250929, released September 29, 2025: a coding- and agent-focused Sonnet launched alongside the Claude Agent SDK.
Claude Sonnet 4 — claude-sonnet-4-20250514, released May 22, 2025: the mid-tier half of the Claude 4 launch, retired June 15, 2026.
Claude 3.7 Sonnet — claude-3-7-sonnet-20250219, released February 24, 2025: the first Claude model with extended thinking, launched with the 📝Claude Code research preview; retired February 19, 2026.
Claude 3.5 Sonnet (October 2024) — claude-3-5-sonnet-20241022, released October 22, 2024: the upgraded 3.5 Sonnet that introduced computer use in public beta, retired October 28, 2025.
Claude 3.5 Sonnet — claude-3-5-sonnet-20240620, released June 20, 2024: outperformed Claude 3 Opus at Sonnet pricing and launched alongside Artifacts; retired October 28, 2025.
Claude 3 Sonnet — claude-3-sonnet-20240229, released March 4, 2024: the mid-tier model of the Claude 3 family, retired July 21, 2025.

Haiku

📝Claude Haiku — Anthropic's fastest, lowest-cost tier, built for high-volume and latency-sensitive work.
Claude Haiku 4.5 — claude-haiku-4-5-20251001, released October 15, 2025: Anthropic's fastest current model and the only one still limited to a 200K-token context window.
Claude 3.5 Haiku — claude-3-5-haiku-20241022, released October 22, 2024: the faster, stronger successor to Claude 3 Haiku, retired February 19, 2026.
Claude 3 Haiku — claude-3-haiku-20240307, released March 13, 2024: the smallest and fastest Claude 3 model, retired April 20, 2026.

Early Claude

Claude 2.1 — claude-2.1, released November 21, 2023: doubled the context window to 200K tokens, retired July 21, 2025.
Claude 2 — claude-2.0, released July 11, 2023: the first Claude model open to the general public through claude.ai, retired July 21, 2025.
Claude Instant — claude-instant-1.2 and earlier, 2023: the faster, lower-cost companion line to Claude 1 and 2, retired November 6, 2024.
Claude 1 — claude-1.3 and earlier, released March 14, 2023: Anthropic's first Claude model, available to selected partners, retired November 6, 2024.