diff --git a/packages/opencode/src/provider/provider.ts b/packages/opencode/src/provider/provider.ts
index 022ec3167956..eeb99dd8c325 100644
--- a/packages/opencode/src/provider/provider.ts
+++ b/packages/opencode/src/provider/provider.ts
@@ -1085,6 +1085,29 @@ export namespace Provider {
           opts.signal = combined
         }
 
+        // For anthropic protocol non-Claude models with interleaved reasoning,
+        // convert thinking blocks to reasoning_content on assistant messages
+        if (
+          typeof model.capabilities.interleaved === "object" &&
+          model.capabilities.interleaved.field &&
+          (model.api.npm === "@ai-sdk/anthropic" || model.api.npm === "@ai-sdk/google-vertex/anthropic") &&
+          opts.body &&
+          opts.method === "POST"
+        ) {
+          const body = JSON.parse(opts.body as string)
+          if (Array.isArray(body.messages)) {
+            const field = model.capabilities.interleaved.field
+            for (const msg of body.messages) {
+              if (msg.role !== "assistant" || !Array.isArray(msg.content)) continue
+              const thinking = msg.content.filter((b: any) => b.type === "thinking")
+              const rest = msg.content.filter((b: any) => b.type !== "thinking")
+              msg[field] = thinking.map((b: any) => b.thinking).join("")
+              msg.content = rest
+            }
+            opts.body = JSON.stringify(body)
+          }
+        }
+
         // Strip openai itemId metadata following what codex does
         // Codex uses #[serde(skip_serializing)] on id fields for all item types:
         // Message, Reasoning, FunctionCall, LocalShellCall, CustomToolCall, WebSearchCall
diff --git a/packages/opencode/src/provider/transform.ts b/packages/opencode/src/provider/transform.ts
index b659799c1b6f..bd60250df159 100644
--- a/packages/opencode/src/provider/transform.ts
+++ b/packages/opencode/src/provider/transform.ts
@@ -135,36 +135,45 @@ export namespace ProviderTransform {
 
     if (typeof model.capabilities.interleaved === "object" && model.capabilities.interleaved.field) {
       const field = model.capabilities.interleaved.field
+      const isAnthropic = model.api.npm === "@ai-sdk/anthropic" || model.api.npm === "@ai-sdk/google-vertex/anthropic"
       return msgs.map((msg) => {
-        if (msg.role === "assistant" && Array.isArray(msg.content)) {
-          const reasoningParts = msg.content.filter((part: any) => part.type === "reasoning")
-          const reasoningText = reasoningParts.map((part: any) => part.text).join("")
+        if (msg.role !== "assistant" || !Array.isArray(msg.content)) return msg
 
-          // Filter out reasoning parts from content
-          const filteredContent = msg.content.filter((part: any) => part.type !== "reasoning")
+        const reasoningText = msg.content
+          .filter((part: any) => part.type === "reasoning")
+          .map((part: any) => part.text)
+          .join("")
+        if (!reasoningText) return msg
 
-          // Include reasoning_content | reasoning_details directly on the message for all assistant messages
-          if (reasoningText) {
-            return {
-              ...msg,
-              content: filteredContent,
-              providerOptions: {
-                ...msg.providerOptions,
-                openaiCompatible: {
-                  ...(msg.providerOptions as any)?.openaiCompatible,
-                  [field]: reasoningText,
-                },
-              },
-            }
-          }
+        const filtered = msg.content.filter((part: any) => part.type !== "reasoning")
 
+        // For anthropic protocol non-Claude models, inject a fake signature so the SDK
+        // emits thinking blocks. The fetch wrapper converts them to reasoning_content.
+        if (isAnthropic) {
           return {
             ...msg,
-            content: filteredContent,
+            content: [
+              {
+                type: "reasoning" as const,
+                text: reasoningText,
+                providerOptions: { anthropic: { signature: "interleaved-placeholder" } },
+              },
+              ...filtered,
+            ],
           }
         }
 
-        return msg
+        return {
+          ...msg,
+          content: filtered,
+          providerOptions: {
+            ...msg.providerOptions,
+            openaiCompatible: {
+              ...(msg.providerOptions as any)?.openaiCompatible,
+              [field]: reasoningText,
+            },
+          },
+        }
       })
     }