`@ai-sdk/anthropic` 3.0.71 rejects `usage.iterations[].type: "fallback_message"` — turn fails with AI_TypeValidationError

[moynzzz]

Description

The bundled @ai-sdk/anthropic@3.0.71 validates usage.iterations[].type as "compaction" | "message". Anthropic now emits "fallback_message" when a response is served by a fallback model (new fallbacks API parameter, e.g. claude-fable-5 → opus). The whole message_delta fails validation and the turn errors out — the assistant can't continue while fallbacks occur.

AI_TypeValidationError: Type validation failed
path: ["usage","iterations",1,"type"]
expected "compaction" | "message", received "fallback_message"

"iterations": [
  { "type": "message", "model": "claude-fable-5", ... },
  { "type": "fallback_message", "model": "claude-opus-4-8", ... }
]

Fixed upstream in vercel/ai#15928, released in @ai-sdk/anthropic@3.0.82 — bumping the pin resolves it.

OpenCode version

1.16.2

Steps to reproduce

1. Use the Anthropic provider with a model where the API serves a fallback (claude-fable-5 with opus fallback)
2. Response usage.iterations contains an entry with type: "fallback_message"
3. Stream fails validation; error repeats on retry while the fallback persists

Operating System

Ubuntu 24.04 (WSL2)

[moynzzz]

A few findings for whoever picks this up:

• Timing: bunfig.toml sets minimumReleaseAge = 259200 (3 days) and @ai-sdk/anthropic is not in minimumReleaseAgeExcludes. 3.0.82 was published 2026-06-09 17:24 UTC, so it can't resolve before 2026-06-12 ~17:25 UTC. Verified locally that the gate also fires with an already-updated lockfile, so a bump PR before that date fails bun install.
• Pins live in three workspaces: packages/opencode (3.0.71), packages/core (3.0.71), packages/console/function (3.0.64). Both packages/opencode/src/provider/provider.ts and packages/core/src/plugin/provider/anthropic.ts import the provider, so the CLI path needs at least those two bumped.
• Pre-validation: with the age gate locally overridden, bumping packages/opencode to 3.0.82 regenerates the lockfile cleanly and tsgo --noEmit passes.

Happy to send the bump PR once the release-age window opens on the 12th.

[kagura-chen]

I can take this — straightforward bump of @ai-sdk/anthropic from 3.0.71 to 3.0.82 which includes the fallback_message iteration type fix (vercel/ai#15928).