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Deprecation & Migration Watch

Intermediate

Models get retired, parameters get renamed, behaviors shift. This page tracks breaking changes so upgrades don't surprise you. If you build on the API, skim it periodically.

Why this matters​

A pinned model ID will eventually be deprecated and then removed. Code that hard-codes it breaks. A little hygiene prevents 2am surprises.

Survival rules​

  • Read model IDs from config, never scatter literals across the codebase — then migrating is a one-line change.
  • Watch announcements for deprecation dates and recommended replacements.
  • Re-run your evals when you switch models — behavior can shift even on a "newer, better" model.
  • Test before the deadline, not after removal.

Common kinds of change​

ChangeExampleWhat to do
Model retiredAn older model ID stops workingMove to the recommended successor; re-eval
Parameter supersededA reasoning/budget knob replaced by effortUpdate calls; see Thinking & Effort
Default shiftA new default model/behaviorPin intentionally; verify your prompts still work
Endpoint/SDK updateNew SDK major versionRead the migration guide; bump deliberately

Current watch​

The authoritative schedule lives on the official model deprecations page — confirm dates there before you migrate. Anthropic gives at least 60 days' notice before retiring a publicly released model.

Deprecated models​

One publicly released Claude model is in the "deprecated, not yet retired" window (checked November 2, 2026): claude-sonnet-4-5-20250929 (Sonnet 4.5) was deprecated September 30, 2026 and retires November 30, 2026. Anthropic's recommended replacement is claude-sonnet-5-5. Calls keep working until the retirement date, then fail — if you still pin this ID, this is your migration, and the window is now under four weeks wide.

Also deprecated: the invitation-only claude-mythos-preview (deprecated June 9, 2026, retirement date to be announced) — move to the current verification-gated model, claude-mythos-5-1. (claude-mythos-5 is still Active, but it has its own migration guide pointing at 5.1, so migrating twice is wasted work.)

claude-haiku-4-5-20251001 is the next ID to watch, and it is now the only model in the lineup past its earliest-possible retirement date: that floor was October 15, 2026, and it has passed (the next one up is Opus 4.5's, on November 24, 2026). It is also listed among the legacy models on the models overview, with a direct successor in claude-haiku-5-5 (released October 7, 2026). As of November 2, 2026 the official status table still lists it as Active with no deprecation announced, so the two readings are not in conflict: "legacy" in Anthropic's own lifecycle vocabulary means no longer receiving updates and may be deprecated in the future, which is one rung before "deprecated." A "not sooner than" date landing is a signal to plan, not an outage — Anthropic commits to at least 60 days' notice, and that clock starts when the notice goes out, not when the floor date passes. Sonnet 4.5 is the worked example: its floor was September 29, 2026, the deprecation notice followed on September 30, and the actual retirement is two months after that. If you pin this ID, the migration is now worth scheduling rather than watching — and it is not a pure ID swap: see Claude Haiku 5.5: The 100K Price Cliff for the five changes that return 400 and the six that return 200. Confirm against the official model status table before you migrate.

Recently retired​

  • claude-opus-4-1-20250805 (Opus 4.1) was retired August 5, 2026 — move to claude-opus-4-8 (or straight to claude-opus-5).
  • claude-opus-4-20250514 (Opus 4) and claude-sonnet-4-20250514 (Sonnet 4) were retired June 15, 2026 — Anthropic's listed replacements are claude-opus-4-8 and claude-sonnet-4-6 respectively (or go straight to claude-opus-5 / claude-sonnet-5).

Calls to any retired ID now return an API error. If your code still pins one of these, that's the first thing to fix.

Parameter deprecations​

The sampling knobs temperature, top_p, and top_k are on their way out, and there are now two different rules depending on which API version you send.

  • Under anthropic-version: 2023-06-01 (what every SDK major released before 21 October 2026 sends): on Claude 4.7-generation models and later — Opus 4.7, Opus 4.8, Opus 5, Opus 5.5, Sonnet 5, Sonnet 5.5, Haiku 5.5, Fable 5, Fable 5.1, Mythos 5, Mythos 5.1 — and on Claude Mythos Preview, setting any of them to a non-default value returns a 400 error. Default values are accepted, and older models still accept non-default values. Mind the version numbers rather than the names: Haiku 5.5 rejects non-default sampling values, while the older Haiku 4.5 still accepts them, as do Opus 4.6 and Sonnet 4.6.
  • Under anthropic-version: 2026-10-21: the three parameters are removed. Sending one returns a 400 on every model, even at the parameter's default value. The newest SDK majors and the ant CLI have dropped them from their request types and flags.

Either way, the fix is the same: omit all three and steer behavior with prompting and Thinking & Effort instead. The one case with no replacement is a deliberately lowered temperature on an older model that still honors it — Anthropic's documented options there are to stop sending the parameter or to keep that request on 2023-06-01. Full breakdown of which version you're on and what else changes with it: API Version 2026-10-21.

Always confirm your model IDs against the Current Models & Pricing table; if you're on an older ID, plan a migration.

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