What’s New
See Anthropic’s model migration guide for a full overview of changes.
Claude 5 Sonnet introduces three major changes versus Sonnet 4.6:
- Sampling parameters removed —
temperature, top_p, and top_k are no longer supported and will be ignored
- Adaptive-only thinking — when reasoning is enabled the only supported mode is adaptive;
thinking.budget_tokens is no longer supported and reasoning.max_tokens is ignored
- New
'xhigh' effort level — a new effort level between 'high' and 'max' via verbosity / output_config.effort
It also adds real-time cyber safeguards.
Sampling Parameters Removed
Claude 5 Sonnet no longer accepts temperature, top_p, or top_k. If you pass these parameters, they will be silently ignored — your request will still succeed, but the parameters will have no effect.
// These parameters are ignored on Claude 5 Sonnet
{
"model": "anthropic/claude-sonnet-5",
"temperature": 0.5,
"top_p": 0.9,
"top_k": 50,
"messages": [{ "role": "user", "content": "Hello" }]
}
Adaptive-Only Thinking
Claude 5 Sonnet supports only adaptive thinking. On Sonnet 4.6, reasoning could be controlled via a token budget (reasoning.max_tokens / thinking.budget_tokens) or left adaptive; on Sonnet 5, budget-based thinking is removed and adaptive is the only remaining mode when reasoning is on. The new API default is adaptive thinking on at effort high.
Reasoning itself remains opt-in on all Anthropic models via reasoning.enabled=true — Sonnet 5 does not change that.
Concretely on Sonnet 5:
reasoning.max_tokens is accepted but ignoredreasoning.effort maps to Anthropic’s output_config.effort (see Parameter Summary) rather than a thinking budgetthinking.budget_tokens is no longer supported upstream
To influence overall response effort (not reasoning-specific), use verbosity. It maps to Anthropic’s output_config.effort and applies whether or not reasoning is enabled.
// Opt in to adaptive thinking — the only thinking mode on Sonnet 5
{
"model": "anthropic/claude-sonnet-5",
"reasoning": { "enabled": true },
"messages": [{ "role": "user", "content": "Solve this problem step by step" }]
}
// reasoning.max_tokens is ignored (adaptive used)
{
"model": "anthropic/claude-sonnet-5",
"reasoning": { "enabled": true, "max_tokens": 10000 },
"messages": [{ "role": "user", "content": "Hello" }]
}
// ↑ Equivalent to just { "reasoning": { "enabled": true } }
// reasoning.effort maps to output_config.effort (thinking stays adaptive)
{
"model": "anthropic/claude-sonnet-5",
"reasoning": { "enabled": true, "effort": "low" },
"messages": [{ "role": "user", "content": "Hello" }]
}
// ↑ Equivalent to { "reasoning": { "enabled": true }, "verbosity": "low" }
New 'xhigh' Effort Level
A new 'xhigh' effort level is available between 'high' and 'max' via the verbosity parameter. This maps to Anthropic’s output_config.effort.
{
"model": "anthropic/claude-sonnet-5",
"verbosity": "xhigh"
}
low → medium → high → xhigh → max.
Sonnet 4.6 supported low, medium, high, and max. Sonnet 5 adds 'xhigh' between 'high' and 'max'. For models that don’t support a given level, it automatically falls back to the next supported level ('xhigh' → 'high').
Cyber Safeguards
Like Opus 4.7 and 4.8, Claude 5 Sonnet ships with real-time cyber classifiers that block some high-risk dual-use activities. Affected requests are refused upstream by Anthropic; OpenRouter surfaces the refusal as-is. See Anthropic’s Real-time cyber safeguards on Claude for details.
Parameter Summary
With sampling parameters and reasoning budgets removed on Sonnet 5, output_config.effort is the remaining lever for influencing overall response effort. You can set it via verbosity, or via reasoning.effort when reasoning is enabled (verbosity wins if both are passed; 'minimal' maps to 'low', and 'none' disables reasoning entirely so no output_config.effort is sent).
| Parameter | Claude 5 Sonnet Behavior |
|---|
temperature, top_p, top_k | Ignored |
reasoning.max_tokens | Ignored (adaptive used) |
reasoning.effort | Sets output_config.effort (when reasoning is enabled) |
verbosity | Sets output_config.effort |
{ "model": "anthropic/claude-sonnet-5", "verbosity": "xhigh" }
Breaking Changes
| Feature | Sonnet 4.6 | Sonnet 5 |
|---|
temperature / top_p / top_k | Supported | Ignored |
Thinking modes (when reasoning.enabled=true) | Adaptive or budget-based | Adaptive only |
reasoning.max_tokens | Sets a thinking budget | Ignored (adaptive used) |
reasoning.effort | Sets output_config.effort | Sets output_config.effort |
'xhigh' effort level | Falls back to 'high' | Supported |
'max' effort level | Supported | Supported |
