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Claude Code (subscription)

The claude provider runs flux against the same backend as the anthropic provider, but authenticates with a Claude Code / Claude Max subscription OAuth token instead of a metered API key. If you already use Claude Code, flux imports its credential automatically — no separate key, and usage bills against the subscription you already pay for.

flux auth status                 # shows `claude` once a credential resolves
flux auth login claude           # or log in explicitly (OAuth)

flux run -m claude "explain the auth flow"        # bare `claude` = claude/sonnet
flux run -m claude/opus "refactor this module"
flux run -m claude/fable "design the migration plan"

The credential resolves in this order: a token stored by flux auth login claude, then an imported Claude Code credential (~/.claude/.credentials.json).

Models​

The short aliases track the current generation of each tier. An explicit id is passed through verbatim, so a newly released model works without a flux upgrade. Model access follows your subscription.

SpecResolves toTier
claude/fableclaude-fable-5Most capable — hardest, long-horizon work
claude/opusclaude-opus-5Frontier coding / agentic
claude/sonnet (and bare claude)claude-sonnet-5Default — speed/quality balance
claude/haikuclaude-haiku-4-5Fastest, cheapest
claude/<full-id>verbatime.g. claude/claude-sonnet-4-6 to pin a previous generation

Request invariants​

flux gates every optional Messages-API field per model, so each spec above works — a request never carries a field its model rejects:

  • Adaptive thinking (thinking: {"type": "adaptive"}) is sent only to models that accept it — the 4.6 family and newer (Fable 5, Opus ≥ 4.6, Sonnet ≥ 4.6). Haiku 4.5 and older models reject it with HTTP 400, so they get no thinking field at all.
  • Effort (output_config.effort) follows the same gate.
  • Sampling params (temperature, top_p) are omitted for the generations that reject them outright (Fable 5, Opus ≥ 4.7, Sonnet ≥ 5) and still sent to models that accept them.
  • Unknown/future ids default to the newest shape (adaptive thinking on, sampling params off), so a new Anthropic generation works on day one.
  • Prompt caching is applied automatically for long contexts.

Subscription-specific invariants on top:

  • Requests authenticate with Authorization: Bearer … plus the anthropic-beta: oauth-2025-04-20 header — never x-api-key.
  • The token is product-gated to Claude Code: flux prefixes the system prompt with the Claude Code identity line, then appends its own system segments.
  • A malformed spec fails client-side with a hint (claude/ → "names provider claude but no model — add one, e.g. claude/sonnet"); it never reaches the API.

Cost reporting​

Subscription turns are marked (sub) in the CLI/TUI cost line and in flux usage: the dollar figure is the equivalent metered cost — what the same tokens would have cost on the anthropic API — not an incremental charge. See Usage & cost.