Beta changedapi/beta
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15451545 Each input message must be an object with a `role` and `content`. You can specify a single `user`-role message, or you can include multiple `user` and `assistant` messages.
15461546
1547 If the final message uses the `assistant` role, the response content will continue immediately from the content in that message. This can be used to constrain part of the model's response.
1547 If the final message uses the `assistant` role, the response content will continue immediately from the content in that message. This can be used to constrain part of the model's response. This is called prefill. On models that don't support prefill, creating a message that ends with a partial `assistant` response returns a 400 error. See [Prefill not supported](https://platform.claude.com/docs/en/api/errors#prefill-not-supported).
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15491549 Example with a single `user` message:
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15631563 ```
15641564
1565 Example with a partially-filled response from Claude:
1565 Example with a partially-filled response from Claude, for models that support prefill:
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15671567 ```json
15681568 [
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45504550 - `"claude-haiku-4-5"`
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4552 Fastest model with near-frontier intelligence
4553
45544552 - `"claude-haiku-4-5-20251001"`
45554553
4556 Fastest model with near-frontier intelligence
4557
45584554 - `"claude-opus-4-5"`
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45604556 Powerful intelligence for long-running agents and coding
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51505146- `fallbacks: optional BetaFallbacksParam or null`
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5152 Opt-in server-side retry on one or more substitute models when the requested model declines for policy reasons. Tried in order: if the first entry also declines, the second is tried, and so on. The string "default" requests the requested model's server-defined default fallback configuration.
5148 Opt-in server-side retry on one or more substitute models when the requested model declines for policy reasons. Tried in order: if the first entry also declines, the second is tried, and so on. Some models don't support fallbacks; on those models, a list of fallback models returns a 400 error. See [Server-side fallback](https://platform.claude.com/docs/en/build-with-claude/refusals-and-fallback#server-side-fallback). The string "default" requests the requested model's server-defined default fallback configuration. On a model that doesn't support fallbacks, the request runs on the requested model alone, so a declined request stays declined.
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51545150 - `array of BetaFallbackParam`
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52485244 - `display: optional "summarized" or "omitted" or "updates" or null`
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5250 Controls how thinking content appears in the response. When set to `summarized`, thinking is returned normally. When set to `omitted`, thinking content is redacted but a signature is returned for multi-turn continuity. Defaults to `summarized`.
5246 Controls how thinking content appears in the response. When set to `summarized`, thinking is returned normally. When set to `omitted`, thinking content is redacted but a signature is returned for multi-turn continuity. The default depends on the model; see [Controlling thinking display](https://platform.claude.com/docs/en/build-with-claude/thinking#controlling-thinking-display).
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52525248 - `"summarized"`
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52745270 - `display: optional "summarized" or "omitted" or "updates" or null`
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5276 Controls how thinking content appears in the response. When set to `summarized`, thinking is returned normally. When set to `omitted`, thinking content is redacted but a signature is returned for multi-turn continuity. Defaults to `summarized`.
5272 Controls how thinking content appears in the response. When set to `summarized`, thinking is returned normally. When set to `omitted`, thinking content is redacted but a signature is returned for multi-turn continuity. The default depends on the model; see [Controlling thinking display](https://platform.claude.com/docs/en/build-with-claude/thinking#controlling-thinking-display).
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52785274 - `"summarized"`
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53805376- `thinking: optional BetaThinkingConfigParam`
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5382 Configuration for enabling Claude's extended thinking.
5378 Configuration for Claude's thinking.
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5384 When enabled, responses include `thinking` content blocks showing Claude's thinking process before the final answer. Requires a minimum budget of 1,024 tokens and counts towards your `max_tokens` limit.
5380 With `{"type": "adaptive"}`, Claude decides when and how much to think. With `{"type": "enabled"}` (manual extended thinking), you set a `budget_tokens` of at least 1,024. Thinking tokens count toward your `max_tokens` limit.
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5386 See [extended thinking](https://platform.claude.com/docs/en/build-with-claude/extended-thinking) for details.
5382 Which `type` values are accepted, and what happens when you omit `thinking`, depend on the model. See [thinking](https://platform.claude.com/docs/en/build-with-claude/thinking#configuring-thinking) for each model's behavior.
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53885384 - `BetaThinkingConfigEnabled object`
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77307726 Name of the tool.
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7732 This is how the tool will be called by the model and in `tool_use` blocks.
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7734 - `allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"`
7735
7736 - `"direct"`
7737
7738 - `"code_execution_20250825"`
7739
7740 - `"code_execution_20260120"`
7741
7742 - `"code_execution_20260521"`
7743
7744 - `cache_control: optional BetaCacheControlEphemeral or null`
7745
7746 Create a cache control breakpoint at this content block.
7747
7748 - `defer_loading: optional boolean`
7749
7750 If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.
7751
7752 - `input_examples: optional array of map[unknown]`
7753
7754 - `strict: optional boolean`
7755
7756 When true,
7728 This is how the tool will be called by
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