Anthropic

Configure Anthropic (Claude) in GoModel and understand how reasoning effort maps to Claude’s adaptive thinking and effort control.

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.

Configure

ANTHROPIC_API_KEY=sk-ant-...
# ANTHROPIC_BASE_URL=https://api.anthropic.com/v1   # optional override
# ANTHROPIC_DEFAULT_MAX_TOKENS=4096                 # injected when callers omit max_tokens

Or in config.yaml:

providers:
  anthropic:
    type: anthropic
    api_key: "${ANTHROPIC_API_KEY}"

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.

Reasoning effort mapping

GoModel accepts OpenAI-shaped "reasoning": {"effort": "..."} and translates it to Claude’s native controls. The five accepted levels are low, medium, high, xhigh, and max; any other value is downgraded to low and logged. The translation depends on whether the model supports adaptive thinking.

Model generation	Thinking config	Effort destination
Adaptive — claude-opus-4-8, claude-opus-4-7, claude-opus-4-6, claude-sonnet-4-6 (and dated snapshots of each)	thinking: {type: "adaptive"}	output_config.effort (passed through)
Legacy (everything else, e.g. claude-opus-4-5, claude-3-5-sonnet)	thinking: {type: "enabled", budget_tokens: N}	mapped to a token budget

Adaptive routing is an explicit allowlist, not a version comparison. New model IDs are treated as legacy until added to the list, so they keep working (via budget_tokens) rather than silently sending an unsupported config.

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:

Effort	Budget tokens
low	5000
medium	10000
high / xhigh / max	20000

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 Opus 4.8 and Opus 4.7, and max on 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 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.

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.