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Anthropic setup is just an API key. This page exists for one quirk: how GoModel maps the OpenAI-style reasoning.effort knob onto Claude’s native thinking and effort controls, which differ by model generation.

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Configure

Or in config.yaml:
Anthropic’s /v1/messages requires max_tokens on every request. GoModel injects ANTHROPIC_DEFAULT_MAX_TOKENS (default 4096) when a caller omits it, keeping the OpenAI-compatible surface lenient.

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Claude subscription (OAuth token)

GoModel also accepts a Claude subscription OAuth token as the Anthropic credential. Generate one with claude setup-token (requires a Claude subscription — Pro, Max, Team, or Enterprise — and the Claude Code CLI) and set it as the provider key:
Tokens with the sk-ant-oat prefix are detected automatically: GoModel sends them as Authorization: Bearer with the oauth-2025-04-20 beta instead of x-api-key. No extra configuration is needed.
Anthropic authorizes subscription OAuth tokens only for Claude Code traffic. Use this to route your own Claude Code through GoModel (see the Claude Code guide); requests from other clients are rejected upstream with “This credential is only authorized for use with Claude Code”. Endpoints outside the Claude Code surface (such as model listing) may also be rejected — if provider model discovery fails, configure the models list for the provider explicitly.

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Reasoning effort mapping

GoModel accepts the OpenAI-shaped "reasoning": {"effort": "..."} object as well as the Chat Completions string form "reasoning_effort": "..." (a non-empty reasoning.effort wins when both are present; an empty object falls back to the string form) and translates them to Claude’s native controls. The five accepted levels are low, medium, high, xhigh, and max; values are matched case-insensitively and any other value is downgraded to low and logged. The translation depends on whether the model supports adaptive thinking.
Adaptive routing is an explicit allowlist, not a version comparison. New model IDs are treated as legacy until added to the list. For pre-4.7 models the legacy fallback keeps working via budget_tokens; models from Opus 4.7 onward reject budget_tokens outright, so a new adaptive-only model ID fails with an upstream 400 until it is added to the allowlist.
For legacy models the effort string maps to a thinking budget; max_tokens is bumped above the budget when needed. xhigh and max are adaptive-only levels, so on legacy models they are capped at the high budget rather than inflating max_tokens past what those models can emit:
Omit reasoning to leave thinking off. On the adaptive models above, GoModel only sets thinking: {type: "adaptive"} when you pass reasoning.effort; without it those models do not engage extended thinking. Effort is a separate control that governs overall token spend (text and tool calls) whether or not thinking is engaged, and Anthropic defaults it to high when unset. It is a behavioral signal for depth and verbosity, not a hard budget — actual usage varies per request and is bounded by max_tokens.
Effort levels are model-gated upstream: xhigh is only available on Fable 5 and Opus 4.8/4.7, and max on Fable 5, Opus 4.8/4.7/4.6, and Sonnet 4.6. GoModel forwards the level you send; Anthropic rejects it with a 400 if the target model does not support it. Manual budget_tokens thinking is rejected on Fable 5 and Opus 4.7/4.8, which is why GoModel uses adaptive thinking for those models.
When extended thinking is engaged, Anthropic requires temperature = 1. GoModel drops any other temperature value (and logs it) rather than failing the request.

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Native passthrough

To send Claude-native request fields that have no OpenAI-compatible equivalent (for example inline mid-task system entries in the messages array), use the passthrough route /p/anthropic/messages, which forwards the body verbatim.
Last modified on August 18, 2026