Request 2 caches its request content (not the response) changedbuild-with-claude/prompt-caching
Nearest release: v2.1.281, published an hour before this site recorded the change. Shown because the two are within 24 hours of each other. Nothing here says the release caused the edit.
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666666| **Thinking parameters** | Model-specific | Model-specific | ✘ | The thinking configuration (mode, and `budget_tokens` in extended mode) is rendered into the prompt, so changing it always invalidates message blocks; tool and system caches are also invalidated on models that render the configuration ahead of them. See [Thinking and prompt caching](https://platform.claude.com/docs/en/build-with-claude/thinking#thinking-and-prompt-caching). |
667667| **Effort setting** | Model-specific | Model-specific | ✘ | Changing the [`output_config.effort`](https://platform.claude.com/docs/en/build-with-claude/effort) value always invalidates message blocks, with the same model-specific effect on tool and system caches as thinking parameters. Setting effort explicitly to the model's default is equivalent to omitting it and does not invalidate. On models that support [per-message effort](https://platform.claude.com/docs/en/build-with-claude/effort#change-effort-mid-conversation-beta), an effort change carried in a `role: "system"` message inside `messages` leaves the cached prefix intact. |
668668| **Non-tool results passed to extended thinking requests** | ✓ | ✓ | Model-specific | On Opus 4.5+ and Sonnet 4.6+, thinking blocks are preserved by default, so the cache remains valid (✓). On earlier Opus/Sonnet models and all Haiku models, all previously-cached thinking blocks are stripped from context, and any messages that follow those thinking blocks are removed from the cache (✘). For more details, see [Caching with thinking blocks](https://platform.claude.com/docs/en/build-with-claude/prompt-caching#caching-with-thinking-blocks). |
669| **Dropped thinking blocks** | ✓ | ✓ | ✘ | When the API drops a Claude Fable 5.1 or Claude Mythos 5.1 thinking block that isn't [preserved](https://platform.claude.com/docs/en/build-with-claude/thinking#preserved-thinking) on that request (for example, one you replay to an earlier model), the cached prefix changes from that block's position onward on that request. Blocks the receiving model can read, passed back unchanged, keep the cache intact. |
669| **Dropped thinking blocks** | ✓ | ✓ | ✘ | When the API drops a Claude Fable 5.1, Claude Mythos 5.1, or Claude Opus 5.5 thinking block that isn't [preserved](https://platform.claude.com/docs/en/build-with-claude/thinking#preserved-thinking) on that request (for example, one you replay to a model that can't read it), the cached prefix changes from that block's position onward on that request. Blocks the receiving model can read, passed back unchanged, keep the cache intact. |
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671671On models that support [mid-conversation tool changes](https://platform.claude.com/docs/en/build-with-claude/mid-conversation-system-messages#mid-conversation-tool-changes), the `inline-tools-2026-09-15` beta header lets you add a tool, or change a tool's definition, partway through a conversation without editing `tools`. Send the definition in a `tool_addition` block in a mid-conversation system message and leave `tools` exactly as you first sent it. The cached prefix still matches, so only the appended message is processed as new input. The one exception is a `tools` array with no non-deferred tool, where the first tool defined this way costs one full cache miss on that request. See [Define tools in a message](https://platform.claude.com/docs/en/build-with-claude/mid-conversation-system-messages#define-tools-in-a-message-beta).
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10661066 messages: [['role' => 'user', 'content' => 'warmup']],
10671067 );
10681068
1069 echo $prewarm->stopReason->value, PHP_EOL; // "max_tokens"
1069 echo $prewarm->stopReason, PHP_EOL; // "max_tokens"
10701070 echo json_encode($prewarm->content), PHP_EOL; // []
10711071 echo json_encode($prewarm->usage), PHP_EOL;
10721072 ```
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