diff --git a/packages/opencode/src/provider/transform.ts b/packages/opencode/src/provider/transform.ts
index 4566fc1de2b..95b9c0ca3b0 100644
--- a/packages/opencode/src/provider/transform.ts
+++ b/packages/opencode/src/provider/transform.ts
@@ -48,27 +48,30 @@ export namespace ProviderTransform {
       })
     }
 
-    // Anthropic rejects messages with empty content - filter out empty string messages
-    // and remove empty text/reasoning parts from array content
-    if (model.api.npm === "@ai-sdk/anthropic") {
-      msgs = msgs
-        .map((msg) => {
-          if (typeof msg.content === "string") {
-            if (msg.content === "") return undefined
-            return msg
-          }
-          if (!Array.isArray(msg.content)) return msg
-          const filtered = msg.content.filter((part) => {
+    // Provider APIs reject messages with empty or whitespace-only content
+    // Filter out empty/whitespace string messages and remove empty text/reasoning parts
+    msgs = msgs
+      .map((msg) => {
+        if (typeof msg.content === "string") {
+          const trimmed = msg.content.trim()
+          if (trimmed === "") return undefined
+          return { ...msg, content: trimmed }
+        }
+        if (!Array.isArray(msg.content)) return msg
+        const filtered = msg.content
+          .map((part) => {
             if (part.type === "text" || part.type === "reasoning") {
-              return part.text !== ""
+              const trimmed = part.text.trim()
+              if (trimmed === "") return undefined
+              return { ...part, text: trimmed }
             }
-            return true
+            return part
           })
-          if (filtered.length === 0) return undefined
-          return { ...msg, content: filtered }
-        })
-        .filter((msg): msg is ModelMessage => msg !== undefined && msg.content !== "")
-    }
+          .filter((part): part is NonNullable<typeof part> => part !== undefined)
+        if (filtered.length === 0) return undefined
+        return { ...msg, content: filtered }
+      })
+      .filter((msg): msg is ModelMessage => msg !== undefined && msg.content !== "")
 
     if (model.api.id.includes("claude")) {
       return msgs.map((msg) => {
diff --git a/packages/opencode/test/provider/transform.test.ts b/packages/opencode/test/provider/transform.test.ts
index 33047b5bcb4..d80eaae67cc 100644
--- a/packages/opencode/test/provider/transform.test.ts
+++ b/packages/opencode/test/provider/transform.test.ts
@@ -448,7 +448,7 @@ describe("ProviderTransform.message - empty image handling", () => {
   })
 })
 
-describe("ProviderTransform.message - anthropic empty content filtering", () => {
+describe("ProviderTransform.message - empty and whitespace content filtering", () => {
   const anthropicModel = {
     id: "anthropic/claude-3-5-sonnet",
     providerID: "anthropic",
@@ -596,7 +596,7 @@ describe("ProviderTransform.message - anthropic empty content filtering", () =>
     expect(result[0].content[1]).toEqual({ type: "text", text: "Result" })
   })
 
-  test("does not filter for non-anthropic providers", () => {
+  test("filters empty content for all providers including OpenAI", () => {
     const openaiModel = {
       ...anthropicModel,
       providerID: "openai",
@@ -608,18 +608,70 @@ describe("ProviderTransform.message - anthropic empty content filtering", () =>
     }
 
     const msgs = [
+      { role: "user", content: "Hello" },
       { role: "assistant", content: "" },
       {
         role: "assistant",
         content: [{ type: "text", text: "" }],
       },
+      { role: "user", content: "World" },
     ] as any[]
 
     const result = ProviderTransform.message(msgs, openaiModel, {})
 
     expect(result).toHaveLength(2)
-    expect(result[0].content).toBe("")
-    expect(result[1].content).toHaveLength(1)
+    expect(result[0].content).toBe("Hello")
+    expect(result[1].content).toBe("World")
+  })
+
+  test("filters whitespace-only string content", () => {
+    const msgs = [
+      { role: "user", content: "Hello" },
+      { role: "assistant", content: "   " },
+      { role: "user", content: "\t\n" },
+      { role: "user", content: "World" },
+    ] as any[]
+
+    const result = ProviderTransform.message(msgs, anthropicModel, {})
+
+    expect(result).toHaveLength(2)
+    expect(result[0].content).toBe("Hello")
+    expect(result[1].content).toBe("World")
+  })
+
+  test("filters whitespace-only text parts from array content", () => {
+    const msgs = [
+      {
+        role: "assistant",
+        content: [
+          { type: "text", text: "   " },
+          { type: "text", text: "Hello" },
+          { type: "text", text: "\t\n" },
+        ],
+      },
+    ] as any[]
+
+    const result = ProviderTransform.message(msgs, anthropicModel, {})
+
+    expect(result).toHaveLength(1)
+    expect(result[0].content).toHaveLength(1)
+    expect(result[0].content[0]).toEqual({ type: "text", text: "Hello" })
+  })
+
+  test("trims whitespace from text content", () => {
+    const msgs = [
+      { role: "user", content: "  Hello World  " },
+      {
+        role: "assistant",
+        content: [{ type: "text", text: "  Response  " }],
+      },
+    ] as any[]
+
+    const result = ProviderTransform.message(msgs, anthropicModel, {})
+
+    expect(result).toHaveLength(2)
+    expect(result[0].content).toBe("Hello World")
+    expect(result[1].content[0]).toEqual({ type: "text", text: "Response" })
   })
 })