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: bf315983c668a6b1f0101c8b7df10e4e44f1a2aa

Author: anthropic-sdks-writer[bot]

anthropic-java-core/src/main/kotlin/com/anthropic/helpers/BetaMessageAccumulator.kt

@@ -311,6 +311,13 @@ class BetaMessageAccumulator private constructor() {
                             .contextManagement(messageDelta.contextManagement().get())
                     }
 
+                    // Only sent on `message_delta` after a mid-stream model fallback, in which case
+                    // it replaces the value from `message_start`.
+                    if (messageDelta.inputTransformations().isPresent) {
+                        requireMessageBuilder()
+                            .inputTransformations(messageDelta.inputTransformations().get())
+                    }
+
                     messageUsage = mergeMessageUsage(requireMessageUsage(), messageDelta.usage())
                 }
 

anthropic-java-core/src/main/kotlin/com/anthropic/helpers/BetaRefusalFallbackInterceptor.kt

@@ -1095,7 +1095,8 @@ private class FallbackStreamSplicer(
      * The initial stream (`splice == null`) is forwarded in its original wire bytes; a spliced hop
      * (`splice` set) has its message_start suppressed (the client already saw the initial one), its
      * block indices shifted by [indexBase], and its terminal message_delta's usage rewritten to the
-     * `usage.iterations` chain shape.
+     * `usage.iterations` chain shape, with that message_start's `input_transformations` copied onto
+     * it.
      *
      * A refusal that can be chained — it carries a `fallback_credit_token` and a fallback entry
      * remains — ends the hop early: open blocks are closed, the terminal message_delta +
@@ -1114,6 +1115,9 @@ private class FallbackStreamSplicer(
         val tracker = BlockTracker(indexBase)
         var model: String? = null
         var startUsage: ObjectNode? = null
+        // `input_transformations` from a spliced fallback's `message_start`, which is not
+        // re-emitted. Copied onto the emitted message_delta, as a server-side fallback does.
+        var startInputTransformations: JsonNode? = null
 
         rawSseHandler(jsonMapper).handle(response).use { sseStream ->
             events@ for (sse in sseStream.stream().asSequence()) {
@@ -1143,6 +1147,10 @@ private class FallbackStreamSplicer(
                             message?._usage()?.asKnown()?.getOrNull()?.let {
                                 jsonMapper.valueToTree<ObjectNode>(it)
                             }
+                        val startMessage = event.path("message")
+                        if (startMessage.has("input_transformations")) {
+                            startInputTransformations = startMessage.get("input_transformations")
+                        }
                         if (splice != null) {
                             continue@events
                         }
@@ -1199,6 +1207,7 @@ private class FallbackStreamSplicer(
                                             deltaEvent,
                                             delta,
                                             details,
+                                            startInputTransformations.takeIf { splice != null },
                                         ),
                                     model,
                                     tracker.blocks,
@@ -1229,6 +1238,12 @@ private class FallbackStreamSplicer(
                             chain.add(entry)
                             usage.set<JsonNode>("iterations", chain)
                             event.set<JsonNode>("usage", usage)
+                            val inputTransformations = startInputTransformations
+                            if (
+                                !event.has("input_transformations") && inputTransformations != null
+                            ) {
+                                event.set<JsonNode>("input_transformations", inputTransformations)
+                            }
                             yield(emit(event))
                             continue@events
                         }
@@ -1317,9 +1332,8 @@ private class FallbackStreamSplicer(
      * `recommended_model` pointed at the hop last tried and its usage backfilled from its
      * message_start (injected raw: the merged usage is the wire shape, not a typed value).
      */
-    private fun heldRefusalDelta(refusal: Refusal, recommendedModel: String): ByteArray =
-        emit(
-            "message_delta",
+    private fun heldRefusalDelta(refusal: Refusal, recommendedModel: String): ByteArray {
+        val builder =
             refusal.event
                 .toBuilder()
                 .delta(
@@ -1331,8 +1345,14 @@ private class FallbackStreamSplicer(
                         .build()
                 )
                 .usage(JsonValue.fromJsonNode(refusal.usage))
-                .build(),
-        )
+        // The spliced fallback's message_start was not re-emitted, so copy its
+        // `input_transformations` onto this delta unless the delta already has its own.
+        val inputTransformations = refusal.inputTransformations
+        if (inputTransformations != null && refusal.event._inputTransformations().isMissing()) {
+            builder.inputTransformations(JsonValue.fromJsonNode(inputTransformations))
+        }
+        return emit("message_delta", builder.build())
+    }
 
     private fun messageStop(): ByteArray =
         emit("message_stop", BetaRawMessageStopEvent.builder().build())
@@ -1434,6 +1454,12 @@ private class FallbackStreamSplicer(
         /** [event]'s delta and refusal stop details, rebuilt into it when it's surfaced. */
         val delta: BetaRawMessageDeltaEvent.Delta,
         val details: BetaRefusalStopDetails,
+        /**
+         * The `input_transformations` from a spliced fallback hop's suppressed `message_start`
+         * event. Retained so the field can be forwarded onto the replayed refusal `message_delta`
+         * event ([event]); `null` for the initial stream.
+         */
+        val inputTransformations: JsonNode?,
     )
 
     /** A response content block being accumulated from its streaming deltas. */

anthropic-java-core/src/main/kotlin/com/anthropic/models/beta/AnthropicBeta.kt

@@ -108,6 +108,17 @@ class AnthropicBeta @JsonCreator private constructor(private val value: JsonFiel
 
         @JvmField val CE_USER_MANAGEMENT_2026_07_13 = of("ce-user-management-2026-07-13")
 
+        @JvmField
+        val MID_CONVERSATION_OUTPUT_CONFIG_2026_07_01 =
+            of("mid-conversation-output-config-2026-07-01")
+
+        @JvmField
+        val THINKING_BINDING_CONTROLS_2026_08_01 = of("thinking-binding-controls-2026-08-01")
+
+        @JvmField
+        val MID_CONVERSATION_SYSTEM_CLEAR_AT_2026_08_21 =
+            of("mid-conversation-system-clear-at-2026-08-21")
+
         @JvmStatic fun of(value: String) = AnthropicBeta(JsonField.of(value))
 
         @JvmSynthetic
@@ -158,6 +169,9 @@ class AnthropicBeta @JsonCreator private constructor(private val value: JsonFiel
         TASK_BUDGETS_2026_03_13,
         THINKING_DISPLAY_UPDATES_2026_08_18,
         CE_USER_MANAGEMENT_2026_07_13,
+        MID_CONVERSATION_OUTPUT_CONFIG_2026_07_01,
+        THINKING_BINDING_CONTROLS_2026_08_01,
+        MID_CONVERSATION_SYSTEM_CLEAR_AT_2026_08_21,
     }
 
     /**
@@ -211,6 +225,9 @@ class AnthropicBeta @JsonCreator private constructor(private val value: JsonFiel
         TASK_BUDGETS_2026_03_13,
         THINKING_DISPLAY_UPDATES_2026_08_18,
         CE_USER_MANAGEMENT_2026_07_13,
+        MID_CONVERSATION_OUTPUT_CONFIG_2026_07_01,
+        THINKING_BINDING_CONTROLS_2026_08_01,
+        MID_CONVERSATION_SYSTEM_CLEAR_AT_2026_08_21,
         /**
          * An enum member indicating that [AnthropicBeta] was instantiated with an unknown value.
          */
@@ -269,6 +286,11 @@ class AnthropicBeta @JsonCreator private constructor(private val value: JsonFiel
             TASK_BUDGETS_2026_03_13 -> Value.TASK_BUDGETS_2026_03_13
             THINKING_DISPLAY_UPDATES_2026_08_18 -> Value.THINKING_DISPLAY_UPDATES_2026_08_18
             CE_USER_MANAGEMENT_2026_07_13 -> Value.CE_USER_MANAGEMENT_2026_07_13
+            MID_CONVERSATION_OUTPUT_CONFIG_2026_07_01 ->
+                Value.MID_CONVERSATION_OUTPUT_CONFIG_2026_07_01
+            THINKING_BINDING_CONTROLS_2026_08_01 -> Value.THINKING_BINDING_CONTROLS_2026_08_01
+            MID_CONVERSATION_SYSTEM_CLEAR_AT_2026_08_21 ->
+                Value.MID_CONVERSATION_SYSTEM_CLEAR_AT_2026_08_21
             else -> Value._UNKNOWN
         }
 
@@ -325,6 +347,11 @@ class AnthropicBeta @JsonCreator private constructor(private val value: JsonFiel
             TASK_BUDGETS_2026_03_13 -> Known.TASK_BUDGETS_2026_03_13
             THINKING_DISPLAY_UPDATES_2026_08_18 -> Known.THINKING_DISPLAY_UPDATES_2026_08_18
             CE_USER_MANAGEMENT_2026_07_13 -> Known.CE_USER_MANAGEMENT_2026_07_13
+            MID_CONVERSATION_OUTPUT_CONFIG_2026_07_01 ->
+                Known.MID_CONVERSATION_OUTPUT_CONFIG_2026_07_01
+            THINKING_BINDING_CONTROLS_2026_08_01 -> Known.THINKING_BINDING_CONTROLS_2026_08_01
+            MID_CONVERSATION_SYSTEM_CLEAR_AT_2026_08_21 ->
+                Known.MID_CONVERSATION_SYSTEM_CLEAR_AT_2026_08_21
             else -> throw AnthropicInvalidDataException("Unknown AnthropicBeta: $value")
         }
 

anthropic-java-core/src/main/kotlin/com/anthropic/models/beta/agents/BetaManagedAgentsModel.kt

@@ -29,6 +29,12 @@ private constructor(private val value: JsonField<String>) : Enum {
 
     companion object {
 
+        /**
+         * Frontier intelligence for ambitious tasks across coding, scientific discovery, and
+         * enterprise workflows
+         */
+        @JvmField val CLAUDE_FABLE_5_1 = of("claude-fable-5-1")
+
         /** High-performance model for coding and agents */
         @JvmField val CLAUDE_SONNET_5 = of("claude-sonnet-5")
 
@@ -77,6 +83,11 @@ private constructor(private val value: JsonField<String>) : Enum {
 
     /** An enum containing [BetaManagedAgentsModel]'s known values. */
     enum class Known {
+        /**
+         * Frontier intelligence for ambitious tasks across coding, scientific discovery, and
+         * enterprise workflows
+         */
+        CLAUDE_FABLE_5_1,
         /** High-performance model for coding and agents */
         CLAUDE_SONNET_5,
         /** Next generation of intelligence for the hardest knowledge work and coding problems */
@@ -115,6 +126,11 @@ private constructor(private val value: JsonField<String>) : Enum {
      * - It was constructed with an arbitrary value using the [of] method.
      */
     enum class Value {
+        /**
+         * Frontier intelligence for ambitious tasks across coding, scientific discovery, and
+         * enterprise workflows
+         */
+        CLAUDE_FABLE_5_1,
         /** High-performance model for coding and agents */
         CLAUDE_SONNET_5,
         /** Next generation of intelligence for the hardest knowledge work and coding problems */
@@ -157,6 +173,7 @@ private constructor(private val value: JsonField<String>) : Enum {
      */
     fun value(): Value =
         when (this) {
+            CLAUDE_FABLE_5_1 -> Value.CLAUDE_FABLE_5_1
             CLAUDE_SONNET_5 -> Value.CLAUDE_SONNET_5
             CLAUDE_FABLE_5 -> Value.CLAUDE_FABLE_5
             CLAUDE_OPUS_5 -> Value.CLAUDE_OPUS_5
@@ -183,6 +200,7 @@ private constructor(private val value: JsonField<String>) : Enum {
      */
     fun known(): Known =
         when (this) {
+            CLAUDE_FABLE_5_1 -> Known.CLAUDE_FABLE_5_1
             CLAUDE_SONNET_5 -> Known.CLAUDE_SONNET_5
             CLAUDE_FABLE_5 -> Known.CLAUDE_FABLE_5
             CLAUDE_OPUS_5 -> Known.CLAUDE_OPUS_5

anthropic-java-core/src/main/kotlin/com/anthropic/models/beta/messages/BetaFallbackParam.kt

@@ -555,6 +555,23 @@ private constructor(
                 }
             )
 
+        fun blockBinding(): Optional<BetaThinkingBlockBinding> =
+            accept(
+                object : Visitor<Optional<BetaThinkingBlockBinding>> {
+                    override fun visitEnabled(
+                        enabled: BetaThinkingConfigEnabled
+                    ): Optional<BetaThinkingBlockBinding> = enabled.blockBinding()
+
+                    override fun visitDisabled(
+                        disabled: BetaThinkingConfigDisabled
+                    ): Optional<BetaThinkingBlockBinding> = Optional.empty()
+
+                    override fun visitAdaptive(
+                        adaptive: BetaThinkingConfigAdaptive
+                    ): Optional<BetaThinkingBlockBinding> = adaptive.blockBinding()
+                }
+            )
+
         fun enabled(): Optional<BetaThinkingConfigEnabled> = Optional.ofNullable(enabled)
 
         fun disabled(): Optional<BetaThinkingConfigDisabled> = Optional.ofNullable(disabled)