feat(opencode): tolerate Anthropic thinking block binding

package.json

@@ -137,6 +137,7 @@
     "electron"
   ],
   "overrides": {
+    "@ai-sdk/anthropic": "3.0.111",
     "@opentui/core": "catalog:",
     "@opentui/keymap": "catalog:",
     "@opentui/solid": "catalog:",
@@ -160,6 +161,8 @@
     "effect@4.0.0-beta.83": "patches/effect@4.0.0-beta.83.patch",
     "@tanstack/virtual-core@3.17.3": "patches/@tanstack%2Fvirtual-core@3.17.3.patch",
     "@ai-sdk/openai-compatible@2.0.41": "patches/@ai-sdk%2Fopenai-compatible@2.0.41.patch",
-    "@ai-sdk/groq@3.0.31": "patches/@ai-sdk%2Fgroq@3.0.31.patch"
+    "@ai-sdk/groq@3.0.31": "patches/@ai-sdk%2Fgroq@3.0.31.patch",
+    "@ai-sdk/anthropic@3.0.111": "patches/@ai-sdk%2Fanthropic@3.0.111.patch",
+    "@ai-sdk/amazon-bedrock@4.0.166": "patches/@ai-sdk%2Famazon-bedrock@4.0.166.patch"
   }
 }

packages/core/package.json

@@ -63,7 +63,7 @@
   "dependencies": {
     "@ai-sdk/alibaba": "1.0.17",
     "@ai-sdk/amazon-bedrock": "4.0.166",
-    "@ai-sdk/anthropic": "3.0.82",
+    "@ai-sdk/anthropic": "3.0.111",
     "@ai-sdk/azure": "3.0.88",
     "@ai-sdk/cerebras": "2.0.41",
     "@ai-sdk/cohere": "3.0.27",

packages/opencode/package.json

@@ -57,7 +57,7 @@
     "@agentclientprotocol/sdk": "0.21.0",
     "@ai-sdk/alibaba": "1.0.17",
     "@ai-sdk/amazon-bedrock": "4.0.166",
-    "@ai-sdk/anthropic": "3.0.82",
+    "@ai-sdk/anthropic": "3.0.111",
     "@ai-sdk/azure": "3.0.88",
     "@ai-sdk/cerebras": "2.0.60",
     "@ai-sdk/cohere": "3.0.27",

packages/opencode/src/provider/transform.ts

@@ -684,6 +684,41 @@ function anthropicOmitsThinking(apiId: string) {
   return anthropicUsesModernAdaptiveThinking(apiId)
 }
 
+// Opus 5, Sonnet 5, Fable 5.x, and Mythos 5.x think without a `thinking` parameter.
+function anthropicThinksByDefault(apiId: string) {
+  const version = /claude-(?:[a-z]+-)?(\d+)(?:[.-](\d{1,2}))?(?:[.@-]|$)/i.exec(apiId)
+  if (!version) return false
+  return Number(version[1]) >= 5
+}
+
+// Fable 5.1 binds each thinking signature to the system prompt, tool list, and
+// messages above it, and rejects the request when any of that changes. opencode
+// re-renders parts of that prefix between turns (system prompt, tools, compaction),
+// so ask the API to drop the affected blocks instead of failing the request.
+// Models that do not run the check accept the field, so it is safe on every Claude.
+// The patched AI SDK adds the thinking-binding-controls beta whenever it is set.
+const ANTHROPIC_BLOCK_BINDING = { prefixMismatchBehavior: "drop_block" }
+
+function anthropicBlockBinding(model: Provider.Model, options: { [x: string]: any }) {
+  if (!model.api.id.toLowerCase().includes("claude")) return options
+  const byDefault = anthropicThinksByDefault(model.api.id)
+  switch (model.api.npm) {
+    case "@ai-sdk/anthropic":
+    case "@ai-sdk/google-vertex/anthropic": {
+      const thinking = options.thinking ?? (byDefault ? { type: "adaptive" } : undefined)
+      if (!thinking || (thinking.type !== "adaptive" && thinking.type !== "enabled")) return options
+      return { ...options, thinking: { ...thinking, blockBinding: ANTHROPIC_BLOCK_BINDING } }
+    }
+    case "@ai-sdk/amazon-bedrock": {
+      const reasoningConfig = options.reasoningConfig ?? (byDefault ? { type: "adaptive" } : undefined)
+      if (!reasoningConfig || (reasoningConfig.type !== "adaptive" && reasoningConfig.type !== "enabled"))
+        return options
+      return { ...options, reasoningConfig: { ...reasoningConfig, blockBinding: ANTHROPIC_BLOCK_BINDING } }
+    }
+  }
+  return options
+}
+
 function googleThinkingLevelEfforts(apiId: string) {
   const id = apiId.toLowerCase()
   if (!id.includes("gemini-3")) return ["low", "high"]
@@ -1363,7 +1398,7 @@ export function providerOptions(model: Provider.Model, options: { [x: string]: a
     usesOpenAIReasoningGate &&
     (model.capabilities.reasoning || options.reasoningEffort !== undefined || options.reasoningSummary !== undefined)
       ? { ...options, forceReasoning: true }
-      : options
+      : anthropicBlockBinding(model, options)
 
   if (model.api.npm === "@ai-sdk/gateway") {
     // Gateway providerOptions are split across two namespaces:

packages/opencode/src/session/processor.ts

@@ -435,6 +435,20 @@ const layer = Layer.effect(
           case "step-finish": {
             const completedSnapshot = yield* snapshot.track()
             yield* Effect.forEach(Object.keys(ctx.reasoningMap), finishReasoning)
+            // Anthropic reports thinking blocks it removed before the model saw the
+            // prompt. Prefix mismatches mean opencode changed history behind a signed
+            // block; log them so the churn can be tracked down.
+            const dropped = isRecord(value.providerMetadata?.anthropic)
+              ? value.providerMetadata.anthropic.inputTransformations
+              : undefined
+            if (Array.isArray(dropped) && dropped.length > 0) {
+              yield* Effect.logWarning("thinking blocks dropped by provider", {
+                sessionID: ctx.sessionID,
+                messageID: ctx.assistantMessage.id,
+                model: ctx.model.id,
+                transformations: JSON.stringify(dropped),
+              })
+            }
             const usage = Session.getUsage({
               model: ctx.model,
               usage: value.usage ?? new Usage({}),