feat(api): add support for claude-fable-5-1 and claude-mythos-5-1

Also adds per-message `output_config` (effort) and `clear_at` on system
messages, and the thinking-block binding controls (beta).

Stainless-Generated-From: 17a4469d9e7162b583cd8cba86cd66660eed3dad

Author: anthropic-sdks-writer[bot]

scripts/mock-spec.json.gz

@@ -11,6 +11,8 @@
  */
 enum BetaManagedAgentsModel: string
 {
+    case CLAUDE_FABLE_5_1 = 'claude-fable-5-1';
+
     case CLAUDE_SONNET_5 = 'claude-sonnet-5';
 
     case CLAUDE_FABLE_5 = 'claude-fable-5';

src/Beta/Agents/BetaManagedAgentsModel.php

@@ -87,4 +87,10 @@ enum AnthropicBeta: string
     case THINKING_DISPLAY_UPDATES_2026_08_18 = 'thinking-display-updates-2026-08-18';
 
     case CE_USER_MANAGEMENT_2026_07_13 = 'ce-user-management-2026-07-13';
+
+    case MID_CONVERSATION_OUTPUT_CONFIG_2026_07_01 = 'mid-conversation-output-config-2026-07-01';
+
+    case THINKING_BINDING_CONTROLS_2026_08_01 = 'thinking-binding-controls-2026-08-01';
+
+    case MID_CONVERSATION_SYSTEM_CLEAR_AT_2026_08_21 = 'mid-conversation-system-clear-at-2026-08-21';
 }

src/Beta/AnthropicBeta.php

@@ -4,6 +4,7 @@
 
 namespace Anthropic\Beta\Messages;
 
+use Anthropic\Core\Attributes\Optional;
 use Anthropic\Core\Attributes\Required;
 use Anthropic\Core\Concerns\SdkModel;
 use Anthropic\Core\Contracts\BaseModel;
@@ -18,6 +19,7 @@
  * @phpstan-import-type BetaDiagnosticsShape from \Anthropic\Beta\Messages\BetaDiagnostics
  * @phpstan-import-type BetaRefusalStopDetailsShape from \Anthropic\Beta\Messages\BetaRefusalStopDetails
  * @phpstan-import-type BetaUsageShape from \Anthropic\Beta\Messages\BetaUsage
+ * @phpstan-import-type BetaThinkingDroppedInputTransformationShape from \Anthropic\Beta\Messages\BetaThinkingDroppedInputTransformation
  *
  * @phpstan-type BetaMessageShape = array{
  *   id: string,
@@ -32,6 +34,7 @@
  *   stopSequence: string|null,
  *   type: 'message',
  *   usage: BetaUsage|BetaUsageShape,
+ *   inputTransformations?: list<BetaThinkingDroppedInputTransformation|BetaThinkingDroppedInputTransformationShape>|null,
  * }
  */
 final class BetaMessage implements BaseModel
@@ -177,6 +180,32 @@ final class BetaMessage implements BaseModel
     #[Required]
     public BetaUsage $usage;
 
+    /**
+     * Changes the API made to the request's input before showing it to the model:
+     * one entry per change, in request order. Today the only entry type is
+     * `thinking_dropped` — a `thinking`, `redacted_thinking` or `connector_text`
+     * block from the request's `messages` that was removed from the prompt instead
+     * of being shown to the model because it failed a binding check. More entry
+     * types may be added over time; ignore types you do not recognize.
+     *
+     * Requires `anthropic-beta: thinking-binding-controls-2026-08-01`. Present on
+     * every such response from a model that supports extended thinking, as `[]`
+     * when nothing was changed; without the beta, blocks are removed all the same
+     * but nothing is reported. Removed blocks contribute nothing to
+     * `usage.input_tokens`. When streaming, the array is final in `message_start`;
+     * the final `message_delta` event carries it only when a server-side model
+     * fallback happened mid-stream, in which case it holds the serving model's
+     * entries and replaces the one in `message_start`.
+     *
+     * @var list<BetaThinkingDroppedInputTransformation>|null $inputTransformations
+     */
+    #[Optional(
+        'input_transformations',
+        list: BetaThinkingDroppedInputTransformation::class,
+        nullable: true,
+    )]
+    public ?array $inputTransformations;
+
     /**
      * `new BetaMessage()` is missing required properties by the API.
      *
@@ -250,6 +279,7 @@ public function parsedOutput(): mixed
      * @param BetaRefusalStopDetails|BetaRefusalStopDetailsShape|null $stopDetails
      * @param BetaStopReason|value-of<BetaStopReason>|null $stopReason
      * @param BetaUsage|BetaUsageShape $usage
+     * @param list<BetaThinkingDroppedInputTransformation|BetaThinkingDroppedInputTransformationShape>|null $inputTransformations
      */
     public static function with(
         string $id,
@@ -262,6 +292,7 @@ public static function with(
         BetaStopReason|string|null $stopReason,
         ?string $stopSequence,
         BetaUsage|array $usage,
+        ?array $inputTransformations = null,
     ): self {
         $self = new self;
 
@@ -276,6 +307,8 @@ public static function with(
         $self['stopSequence'] = $stopSequence;
         $self['usage'] = $usage;
 
+        null !== $inputTransformations && $self['inputTransformations'] = $inputTransformations;
+
         return $self;
     }
 
@@ -489,4 +522,31 @@ public function withUsage(BetaUsage|array $usage): self
 
         return $self;
     }
+
+    /**
+     * Changes the API made to the request's input before showing it to the model:
+     * one entry per change, in request order. Today the only entry type is
+     * `thinking_dropped` — a `thinking`, `redacted_thinking` or `connector_text`
+     * block from the request's `messages` that was removed from the prompt instead
+     * of being shown to the model because it failed a binding check. More entry
+     * types may be added over time; ignore types you do not recognize.
+     *
+     * Requires `anthropic-beta: thinking-binding-controls-2026-08-01`. Present on
+     * every such response from a model that supports extended thinking, as `[]`
+     * when nothing was changed; without the beta, blocks are removed all the same
+     * but nothing is reported. Removed blocks contribute nothing to
+     * `usage.input_tokens`. When streaming, the array is final in `message_start`;
+     * the final `message_delta` event carries it only when a server-side model
+     * fallback happened mid-stream, in which case it holds the serving model's
+     * entries and replaces the one in `message_start`.
+     *
+     * @param list<BetaThinkingDroppedInputTransformation|BetaThinkingDroppedInputTransformationShape>|null $inputTransformations
+     */
+    public function withInputTransformations(?array $inputTransformations): self
+    {
+        $self = clone $this;
+        $self['inputTransformations'] = $inputTransformations;
+
+        return $self;
+    }
 }

src/Beta/Messages/BetaMessage.php

@@ -4,18 +4,24 @@
 
 namespace Anthropic\Beta\Messages;
 
+use Anthropic\Beta\Messages\BetaMessageParam\ClearAt;
 use Anthropic\Beta\Messages\BetaMessageParam\Content;
 use Anthropic\Beta\Messages\BetaMessageParam\Role;
+use Anthropic\Core\Attributes\Optional;
 use Anthropic\Core\Attributes\Required;
 use Anthropic\Core\Concerns\SdkModel;
 use Anthropic\Core\Contracts\BaseModel;
 
 /**
  * @phpstan-import-type ContentVariants from \Anthropic\Beta\Messages\BetaMessageParam\Content
  * @phpstan-import-type ContentShape from \Anthropic\Beta\Messages\BetaMessageParam\Content
+ * @phpstan-import-type BetaSystemMessageOutputConfigShape from \Anthropic\Beta\Messages\BetaSystemMessageOutputConfig
  *
  * @phpstan-type BetaMessageParamShape = array{
- *   content: ContentShape, role: Role|value-of<Role>
+ *   content: ContentShape,
+ *   role: Role|value-of<Role>,
+ *   clearAt?: null|ClearAt|value-of<ClearAt>,
+ *   outputConfig?: null|BetaSystemMessageOutputConfig|BetaSystemMessageOutputConfigShape,
  * }
  */
 final class BetaMessageParam implements BaseModel
@@ -31,6 +37,24 @@ final class BetaMessageParam implements BaseModel
     #[Required(enum: Role::class)]
     public string $role;
 
+    /**
+     * How long this system message's text stays in front of the model. `"never"` (the default) renders it on every request that includes it. `"next_user_message"` renders it only for the user turn it follows: once a later `role: "user"` message exists in `messages` the message stays in the array (send it unchanged) but is no longer shown to the model. Only permitted on `role: "system"` messages.
+     *
+     * @var value-of<ClearAt>|null $clearAt
+     */
+    #[Optional('clear_at', enum: ClearAt::class, nullable: true)]
+    public ?string $clearAt;
+
+    /**
+     * Per-message output configuration on a role:"system" input message.
+     *
+     * Fields here apply per-turn; ``format`` remains top-level only. An
+     * empty ``{}`` is accepted on a message that carries content; a message
+     * with neither content nor output_config fields is rejected.
+     */
+    #[Optional('output_config', nullable: true)]
+    public ?BetaSystemMessageOutputConfig $outputConfig;
+
     /**
      * `new BetaMessageParam()` is missing required properties by the API.
      *
@@ -57,14 +81,23 @@ public function __construct()
      *
      * @param ContentShape $content
      * @param Role|value-of<Role> $role
+     * @param ClearAt|value-of<ClearAt>|null $clearAt
+     * @param BetaSystemMessageOutputConfig|BetaSystemMessageOutputConfigShape|null $outputConfig
      */
-    public static function with(string|array $content, Role|string $role): self
-    {
+    public static function with(
+        string|array $content,
+        Role|string $role,
+        ClearAt|string|null $clearAt = null,
+        BetaSystemMessageOutputConfig|array|null $outputConfig = null,
+    ): self {
         $self = new self;
 
         $self['content'] = $content;
         $self['role'] = $role;
 
+        null !== $clearAt && $self['clearAt'] = $clearAt;
+        null !== $outputConfig && $self['outputConfig'] = $outputConfig;
+
         return $self;
     }
 
@@ -89,4 +122,35 @@ public function withRole(Role|string $role): self
 
         return $self;
     }
+
+    /**
+     * How long this system message's text stays in front of the model. `"never"` (the default) renders it on every request that includes it. `"next_user_message"` renders it only for the user turn it follows: once a later `role: "user"` message exists in `messages` the message stays in the array (send it unchanged) but is no longer shown to the model. Only permitted on `role: "system"` messages.
+     *
+     * @param ClearAt|value-of<ClearAt>|null $clearAt
+     */
+    public function withClearAt(ClearAt|string|null $clearAt): self
+    {
+        $self = clone $this;
+        $self['clearAt'] = $clearAt;
+
+        return $self;
+    }
+
+    /**
+     * Per-message output configuration on a role:"system" input message.
+     *
+     * Fields here apply per-turn; ``format`` remains top-level only. An
+     * empty ``{}`` is accepted on a message that carries content; a message
+     * with neither content nor output_config fields is rejected.
+     *
+     * @param BetaSystemMessageOutputConfig|BetaSystemMessageOutputConfigShape|null $outputConfig
+     */
+    public function withOutputConfig(
+        BetaSystemMessageOutputConfig|array|null $outputConfig
+    ): self {
+        $self = clone $this;
+        $self['outputConfig'] = $outputConfig;
+
+        return $self;
+    }
 }

src/Beta/Messages/BetaMessageParam.php

@@ -0,0 +1,15 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Anthropic\Beta\Messages\BetaMessageParam;
+
+/**
+ * How long this system message's text stays in front of the model. `"never"` (the default) renders it on every request that includes it. `"next_user_message"` renders it only for the user turn it follows: once a later `role: "user"` message exists in `messages` the message stays in the array (send it unchanged) but is no longer shown to the model. Only permitted on `role: "system"` messages.
+ */
+enum ClearAt: string
+{
+    case NEXT_USER_MESSAGE = 'next_user_message';
+
+    case NEVER = 'never';
+}

src/Beta/Messages/BetaMessageParam/ClearAt.php

@@ -5,6 +5,7 @@
 namespace Anthropic\Beta\Messages;
 
 use Anthropic\Beta\Messages\BetaRawMessageDeltaEvent\Delta;
+use Anthropic\Core\Attributes\Optional;
 use Anthropic\Core\Attributes\Required;
 use Anthropic\Core\Concerns\SdkModel;
 use Anthropic\Core\Contracts\BaseModel;
@@ -13,12 +14,14 @@
  * @phpstan-import-type BetaContextManagementResponseShape from \Anthropic\Beta\Messages\BetaContextManagementResponse
  * @phpstan-import-type DeltaShape from \Anthropic\Beta\Messages\BetaRawMessageDeltaEvent\Delta
  * @phpstan-import-type BetaMessageDeltaUsageShape from \Anthropic\Beta\Messages\BetaMessageDeltaUsage
+ * @phpstan-import-type BetaThinkingDroppedInputTransformationShape from \Anthropic\Beta\Messages\BetaThinkingDroppedInputTransformation
  *
  * @phpstan-type BetaRawMessageDeltaEventShape = array{
  *   contextManagement: null|BetaContextManagementResponse|BetaContextManagementResponseShape,
  *   delta: Delta|DeltaShape,
  *   type: 'message_delta',
  *   usage: BetaMessageDeltaUsage|BetaMessageDeltaUsageShape,
+ *   inputTransformations?: list<BetaThinkingDroppedInputTransformation|BetaThinkingDroppedInputTransformationShape>|null,
  * }
  */
 final class BetaRawMessageDeltaEvent implements BaseModel
@@ -53,6 +56,32 @@ final class BetaRawMessageDeltaEvent implements BaseModel
     #[Required]
     public BetaMessageDeltaUsage $usage;
 
+    /**
+     * Changes the API made to the request's input before showing it to the model:
+     * one entry per change, in request order. Today the only entry type is
+     * `thinking_dropped` — a `thinking`, `redacted_thinking` or `connector_text`
+     * block from the request's `messages` that was removed from the prompt instead
+     * of being shown to the model because it failed a binding check. More entry
+     * types may be added over time; ignore types you do not recognize.
+     *
+     * Requires `anthropic-beta: thinking-binding-controls-2026-08-01`. Present on
+     * every such response from a model that supports extended thinking, as `[]`
+     * when nothing was changed; without the beta, blocks are removed all the same
+     * but nothing is reported. Removed blocks contribute nothing to
+     * `usage.input_tokens`. When streaming, the array is final in `message_start`;
+     * the final `message_delta` event carries it only when a server-side model
+     * fallback happened mid-stream, in which case it holds the serving model's
+     * entries and replaces the one in `message_start`.
+     *
+     * @var list<BetaThinkingDroppedInputTransformation>|null $inputTransformations
+     */
+    #[Optional(
+        'input_transformations',
+        list: BetaThinkingDroppedInputTransformation::class,
+        nullable: true,
+    )]
+    public ?array $inputTransformations;
+
     /**
      * `new BetaRawMessageDeltaEvent()` is missing required properties by the API.
      *
@@ -83,18 +112,22 @@ public function __construct()
      * @param BetaContextManagementResponse|BetaContextManagementResponseShape|null $contextManagement
      * @param Delta|DeltaShape $delta
      * @param BetaMessageDeltaUsage|BetaMessageDeltaUsageShape $usage
+     * @param list<BetaThinkingDroppedInputTransformation|BetaThinkingDroppedInputTransformationShape>|null $inputTransformations
      */
     public static function with(
         BetaContextManagementResponse|array|null $contextManagement,
         Delta|array $delta,
         BetaMessageDeltaUsage|array $usage,
+        ?array $inputTransformations = null,
     ): self {
         $self = new self;
 
         $self['contextManagement'] = $contextManagement;
         $self['delta'] = $delta;
         $self['usage'] = $usage;
 
+        null !== $inputTransformations && $self['inputTransformations'] = $inputTransformations;
+
         return $self;
     }
 
@@ -154,4 +187,31 @@ public function withUsage(BetaMessageDeltaUsage|array $usage): self
 
         return $self;
     }
+
+    /**
+     * Changes the API made to the request's input before showing it to the model:
+     * one entry per change, in request order. Today the only entry type is
+     * `thinking_dropped` — a `thinking`, `redacted_thinking` or `connector_text`
+     * block from the request's `messages` that was removed from the prompt instead
+     * of being shown to the model because it failed a binding check. More entry
+     * types may be added over time; ignore types you do not recognize.
+     *
+     * Requires `anthropic-beta: thinking-binding-controls-2026-08-01`. Present on
+     * every such response from a model that supports extended thinking, as `[]`
+     * when nothing was changed; without the beta, blocks are removed all the same
+     * but nothing is reported. Removed blocks contribute nothing to
+     * `usage.input_tokens`. When streaming, the array is final in `message_start`;
+     * the final `message_delta` event carries it only when a server-side model
+     * fallback happened mid-stream, in which case it holds the serving model's
+     * entries and replaces the one in `message_start`.
+     *
+     * @param list<BetaThinkingDroppedInputTransformation|BetaThinkingDroppedInputTransformationShape>|null $inputTransformations
+     */
+    public function withInputTransformations(?array $inputTransformations): self
+    {
+        $self = clone $this;
+        $self['inputTransformations'] = $inputTransformations;
+
+        return $self;
+    }
 }