{
  "asOf": "2026-10-15",
  "dateDefinition": "First documented external availability, including explicitly labeled restricted previews. Announcement dates and API snapshot suffixes are recorded separately. Not a claim about internal training completion or every platform's rollout.",
  "releases": [
    {"name":"Claude 1.0","family":"Legacy","date":"2023-03-14","announcementDate":"2023-03-14","access":"Initial external launch","source":"https://www.anthropic.com/news/introducing-claude","note":"Launched as Claude; Anthropic's retirement ledger identifies claude-1.0."},
    {"name":"Claude Instant 1.0","family":"Legacy","date":"2023-03-14","announcementDate":"2023-03-14","access":"Initial external launch","source":"https://www.anthropic.com/news/introducing-claude","note":"Launched alongside Claude; retirement ledger identifies claude-instant-1.0."},
    {"name":"Claude 2.0","family":"Legacy","date":"2023-07-11","announcementDate":"2023-07-11","access":"API and public chat beta","source":"https://www.anthropic.com/news/claude-2","note":"Initially offered public chat in the US and UK."},
    {"name":"Claude Instant 1.2","family":"Legacy","date":"2023-08-09","announcementDate":"2023-08-09","access":"API","source":"https://www.anthropic.com/news/releasing-claude-instant-1-2","note":"Distinct from Instant 1.1."},
    {"name":"Claude 2.1","family":"Legacy","date":"2023-11-21","announcementDate":"2023-11-21","access":"API and Claude.ai","source":"https://www.anthropic.com/news/claude-2-1","note":"200K context window."},
    {"name":"Claude 3 Opus","family":"Opus","date":"2024-03-04","announcementDate":"2024-03-04","access":"API and Claude.ai","source":"https://www.anthropic.com/research/claude-3-family","note":"API snapshot 20240229 is earlier than the launch."},
    {"name":"Claude 3 Sonnet","family":"Sonnet","date":"2024-03-04","announcementDate":"2024-03-04","access":"API and Claude.ai","source":"https://www.anthropic.com/research/claude-3-family","note":"Launched together with Opus; Haiku was still forthcoming."},
    {"name":"Claude 3 Haiku","family":"Haiku","date":"2024-03-13","announcementDate":"2024-03-04","access":"API and Claude Pro","source":"https://www.anthropic.com/news/claude-3-haiku","note":"Announced with the family March 4; available March 13. Snapshot 20240307 is not the launch."},
    {"name":"Claude 3.5 Sonnet (June)","family":"Sonnet","date":"2024-06-20","announcementDate":"2024-06-20","access":"Documented availability on Bedrock","source":"https://aws.amazon.com/blogs/aws/anthropics-claude-3-5-sonnet-model-now-available-in-amazon-bedrock-the-most-intelligent-claude-model-yet/","corroboratingSource":"https://www.anthropic.com/news/claude-3-5-sonnet","note":"AWS's contemporaneous launch post and Anthropic's model-card addendum date this June 20; the currently rendered Anthropic news page displays June 21. Earliest documented availability is used."},
    {"name":"Claude 3.5 Sonnet (October)","family":"Sonnet","date":"2024-10-22","announcementDate":"2024-10-22","access":"API and Claude apps","source":"https://www.anthropic.com/news/3-5-models-and-computer-use","note":"An upgraded model, not a repeat announcement. Some Anthropic research calls this version Claude 3.6 Sonnet."},
    {"name":"Claude 3.5 Haiku","family":"Haiku","date":"2024-11-04","announcementDate":"2024-10-22","access":"Documented availability on Bedrock","source":"https://aws.amazon.com/about-aws/whats-new/2024/11/anthropics-claude-3-5-haiku-model-amazon-bedrock/","corroboratingSource":"https://www.anthropic.com/news/3-5-models-and-computer-use","note":"October 22 was the announcement and snapshot date; AWS confirms November 4 availability. This date does not establish every platform's first availability."},
    {"name":"Claude 3.7 Sonnet","family":"Sonnet","date":"2025-02-24","announcementDate":"2025-02-24","access":"API and Claude apps","source":"https://www.anthropic.com/news/claude-3-7-sonnet","note":"Launched alongside the Claude Code research preview; snapshot 20250219 is earlier."},
    {"name":"Claude Opus 4","family":"Opus","date":"2025-05-22","announcementDate":"2025-05-22","access":"API and Claude apps","source":"https://www.anthropic.com/news/claude-4","note":"Joint launch with Sonnet 4; snapshot 20250514 is earlier."},
    {"name":"Claude Sonnet 4","family":"Sonnet","date":"2025-05-22","announcementDate":"2025-05-22","access":"API and Claude apps","source":"https://www.anthropic.com/news/claude-4","note":"Joint launch with Opus 4."},
    {"name":"Claude Opus 4.1","family":"Opus","date":"2025-08-05","announcementDate":"2025-08-05","access":"API and paid Claude plans","source":"https://www.anthropic.com/news/claude-opus-4-1","note":"Agentic coding and reasoning update."},
    {"name":"Claude Sonnet 4.5","family":"Sonnet","date":"2025-09-29","announcementDate":"2025-09-29","access":"API and Claude apps","source":"https://www.anthropic.com/news/claude-sonnet-4-5","note":"Launched with Claude Agent SDK updates."},
    {"name":"Claude Haiku 4.5","family":"Haiku","date":"2025-10-15","announcementDate":"2025-10-15","access":"API and Claude apps","source":"https://www.anthropic.com/news/claude-haiku-4-5","note":"Snapshot 20251001 is earlier than the launch."},
    {"name":"Claude Opus 4.5","family":"Opus","date":"2025-11-24","announcementDate":"2025-11-24","access":"API and Claude apps","source":"https://www.anthropic.com/news/claude-opus-4-5","note":"Snapshot 20251101 is earlier than the launch."},
    {"name":"Claude Opus 4.6","family":"Opus","date":"2026-02-05","announcementDate":"2026-02-05","access":"API and Claude apps","source":"https://www.anthropic.com/news/claude-opus-4-6","note":"First Opus with a 1M context window in beta."},
    {"name":"Claude Sonnet 4.6","family":"Sonnet","date":"2026-02-17","announcementDate":"2026-02-17","access":"API and Claude apps","source":"https://www.anthropic.com/news/claude-sonnet-4-6","note":"1M context window in beta."},
    {"name":"Claude Mythos Preview","family":"Mythos","date":"2026-04-07","announcementDate":"2026-04-07","access":"Restricted research preview","source":"https://www.anthropic.com/research/mythos-preview","note":"External access through Project Glasswing; not general availability."},
    {"name":"Claude Opus 4.7","family":"Opus","date":"2026-04-16","announcementDate":"2026-04-16","access":"General availability","source":"https://www.anthropic.com/news/claude-opus-4-7","note":"Broadly available, distinct from restricted Mythos Preview."},
    {"name":"Claude Opus 4.8","family":"Opus","date":"2026-05-28","announcementDate":"2026-05-28","access":"General availability","source":"https://www.anthropic.com/news/claude-opus-4-8","note":"Successor to Opus 4.7."},
    {"name":"Claude Fable 5","family":"Fable","date":"2026-06-09","announcementDate":"2026-06-09","access":"General-use launch; subsequently suspended","source":"https://www.anthropic.com/news/claude-fable-5-mythos-5","note":"Access suspended June 12 and restored July 1. Relaunch is not counted as a second model."},
    {"name":"Claude Mythos 5","family":"Mythos","date":"2026-06-09","announcementDate":"2026-06-09","access":"Restricted trusted access","source":"https://www.anthropic.com/news/claude-fable-5-mythos-5","note":"Joint launch with Fable 5; access suspended June 12 and restored July 1. Not a general-use model."},
    {"name":"Claude Sonnet 5","family":"Sonnet","date":"2026-06-30","announcementDate":"2026-06-30","access":"General availability","source":"https://www.anthropic.com/news/claude-sonnet-5","note":"Successor to Sonnet 4.6."},
    {"name":"Claude Opus 5","family":"Opus","date":"2026-07-24","announcementDate":"2026-07-24","access":"General availability","source":"https://www.anthropic.com/news/claude-opus-5","note":"Successor to Opus 4.8."},
    {"name":"Claude Fable 5.1","family":"Fable","date":"2026-09-01","announcementDate":"2026-09-01","access":"General availability","source":"https://www.anthropic.com/claude-fable-and-mythos-5-1","corroboratingSource":"https://www.anthropic.com/claude/fable","note":"Feature page displays September 2026; the official Fable model page and newsroom give September 1."},
    {"name":"Claude Mythos 5.1","family":"Mythos","date":"2026-09-01","announcementDate":"2026-09-01","access":"Restricted trusted access","source":"https://www.anthropic.com/claude-fable-and-mythos-5-1","corroboratingSource":"https://www.anthropic.com/claude/mythos","note":"Same underlying model as Fable 5.1 with different safeguards; official Mythos model page gives September 1."},
    {"name":"Claude Opus 5.5","family":"Opus","date":"2026-09-22","announcementDate":"2026-09-22","access":"General availability","source":"https://www.anthropic.com/claude-opus-5-5","note":"The first release in Anthropic's Claude 5.5 family."},
    {"name":"Claude Sonnet 5.5","family":"Sonnet","date":"2026-09-28","announcementDate":"2026-09-28","access":"General availability","source":"https://www.anthropic.com/claude-sonnet-5-5","note":"Second release in the 5.5 family."},
    {"name":"Claude Haiku 5.5","family":"Haiku","date":"2026-10-07","announcementDate":"2026-10-07","access":"General availability","source":"https://www.anthropic.com/claude-haiku-5-5","note":"Previous published Haiku was 4.5; no separate Haiku 5 launch was verified."}
  ],
  "undatedVersions": [
    {"name":"Claude 1.1","date":null,"source":"https://docs.anthropic.com/en/docs/about-claude/model-deprecations","note":"Official retirement ledger confirms the version; an exact launch day was not verified."},
    {"name":"Claude 1.2","date":null,"source":"https://docs.anthropic.com/en/docs/about-claude/model-deprecations","note":"Official retirement ledger confirms the version; an exact launch day was not verified. May 11, 2023 was a context-window announcement, not sufficient evidence for a numbered model launch."},
    {"name":"Claude 1.3","date":null,"source":"https://www.anthropic.com/news/claude-2-amazon-bedrock","note":"Anthropic says 1.3 was available when Bedrock launched in April 2023. This establishes availability by April, not the exact first launch day."},
    {"name":"Claude Instant 1.1","date":null,"source":"https://www.anthropic.com/news/releasing-claude-instant-1-2","note":"The August 9, 2023 Instant 1.2 announcement confirms its predecessor; an exact launch day was not verified."}
  ],
  "forecast": {
    "target":"Claude Fable 5.5",
    "status":"Unannounced in the official sources reviewed as of 2026-10-15; name and launch are assumptions",
    "anchor":"2026-09-01",
    "recentOpusNames":["Claude Opus 4.5","Claude Opus 4.6","Claude Opus 4.7","Claude Opus 4.8","Claude Opus 5","Claude Opus 5.5"],
    "recentSonnetNames":["Claude Sonnet 5","Claude Sonnet 5.5"],
    "fableNames":["Claude Fable 5","Claude Fable 5.1"],
    "method":"Equal-weight average of (a) median of the five most recent Opus update gaps plus the latest Sonnet and Fable gaps, and (b) the sole Fable-to-Fable gap; round to whole days and add to Fable 5.1's initial launch date. A transparent editorial heuristic, not a fitted or calibrated probability model.",
    "watchWindowStart":"2026-11-01",
    "watchWindowEnd":"2026-12-15",
    "windowMeaning":"Subjective monitoring window, not a statistical confidence interval",
    "confidence":"Low",
    "caveats":["Only one observed Fable update interval","Fable and Mythos paired launches are not independent observations","Opus and Sonnet are cross-tier proxies, not equivalent release processes","Initial Fable 5 access was suspended and restored","Anthropic could choose a different version name or skip 5.5","Safety, capacity and launch decisions are not observable from dates"]
  }
}