By 7 October 2026 Anthropic had announced Opus 5.5, Sonnet 5.5 and Haiku 5.5, at different dates and for different service goals. The company positions Opus toward difficult agentic or judgment-intensive work, Sonnet toward broad professional production and Haiku toward responsive, high-volume tasks. These are descriptions of intent and vendor evaluations, not guarantees that one model will win a company-specific benchmark.
Release chronology matters
Anthropic dated the Opus 5.5 introduction to 22 September 2026, Sonnet 5.5 to 28 September, and Haiku 5.5 to 7 October. A product page published later may show updated specifications; do not retroactively attach those details to initial launch day without contemporaneous evidence. Store each release separately in the index. The Claude 4.6 generation introduced dateless model IDs that represent fixed snapshots; that rule cannot safely be generalized to arbitrary shortcuts from much older generations.
Choose by error cost, not adjectives
For contract review or critical analysis, test model quality on annotated cases and track unsupported claims. For production summarization, compare output validity and review time. For triage or routing, small models might suffice if false negatives are controlled. The most expensive failure is not always token spend: wrong tool actions, missed exceptions, delayed processing and operator burden can dominate.
Multimodality and deployment
Do not infer voice or video generation from the fact that a Claude model accepts visual inputs. Document each input/output direction in the API reference for the exact ID. Availability across the Anthropic API, Bedrock, Vertex or other services must be checked independently because IDs, operational limits and regions can differ. Some later model reference pages reflect post-release updates; keep retrieval date alongside the publication date.
What to archive
Save release URL, provider-level model ID, endpoint name, date and any published deprecation notice. Then perform model-on-model evaluations under one prompt, one tool schema and one scoring version. Keep self-reported benchmarks clearly labeled; an enterprise pilot should use the company’s real task distribution.
What to verify before adopting this model or method
Use the exact release ID and API endpoint; confirm your geographic processing location, entitlement tier, model lifecycle, feature flags, context and output limits from the provider console. Run a reproducible evaluation on your own data and retain human oversight for consequential actions. Where a specification, price, commercial license or entitlement is not verified for your deployment, this article deliberately leaves it unasserted instead of filling a plausible number.
Documentation clarification (25 October 2026)
Anthropic’s current model index lists Opus 5.5, Sonnet 5.5 and Haiku 5.5, while Fable 5.1 is a distinct high-reasoning line. Model names, release days and platform-specific identifiers should remain separate database fields.
Sources & Further Reading
- www.anthropic.com — documentation/reference (supplier-provided reference; not independently checked in this pass)
- www.anthropic.com — documentation/reference (supplier-provided reference; not independently checked in this pass)
- Anthropic model IDs and versioning (retrieved from first-party public documentation on 2026-10-25; this is not a deployment test)
- platform.claude.com — documentation/reference (supplier-provided reference; not independently checked in this pass)
- Anthropic Claude models overview (retrieved from first-party public documentation on 2026-10-25; this is not a deployment test)
Source documentation establishes vendor-published facts, not independently measured model quality, tenant access, contractual rights or current prices. Use a dated pricing ledger and an account-specific entitlement check for deployment decisions.