diff --git a/packages/opencode/src/provider/transform.ts b/packages/opencode/src/provider/transform.ts
index c402238685f9..b383c81ab740 100644
--- a/packages/opencode/src/provider/transform.ts
+++ b/packages/opencode/src/provider/transform.ts
@@ -20,6 +20,22 @@ function mimeToModality(mime: string): Modality | undefined {
 export namespace ProviderTransform {
   export const OUTPUT_TOKEN_MAX = Flag.OPENCODE_EXPERIMENTAL_OUTPUT_TOKEN_MAX || 32_000
 
+  // Detects whether a model targets the Anthropic/Claude API regardless of
+  // the SDK package used to reach it (direct, proxy, vertex, bedrock, etc.).
+  function isClaudeModel(model: Provider.Model): boolean {
+    return (
+      model.providerID === "anthropic" ||
+      model.providerID === "google-vertex-anthropic" ||
+      model.api.id.includes("anthropic") ||
+      model.api.id.includes("claude") ||
+      model.id.includes("anthropic") ||
+      model.id.includes("claude") ||
+      model.api.npm === "@ai-sdk/anthropic" ||
+      model.api.npm === "@ai-sdk/google-vertex/anthropic" ||
+      model.api.npm === "@ai-sdk/amazon-bedrock"
+    )
+  }
+
   // Maps npm package to the key the AI SDK expects for providerOptions
   function sdkKey(npm: string): string | undefined {
     switch (npm) {
@@ -51,9 +67,7 @@ export namespace ProviderTransform {
     model: Provider.Model,
     options: Record<string, unknown>,
   ): ModelMessage[] {
-    // 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" || model.api.npm === "@ai-sdk/amazon-bedrock") {
+    if (isClaudeModel(model)) {
       msgs = msgs
         .map((msg) => {
           if (typeof msg.content === "string") {
@@ -73,7 +87,7 @@ export namespace ProviderTransform {
         .filter((msg): msg is ModelMessage => msg !== undefined && msg.content !== "")
     }
 
-    if (model.api.id.includes("claude")) {
+    if (isClaudeModel(model)) {
       const scrub = (id: string) => id.replace(/[^a-zA-Z0-9_-]/g, "_")
       return msgs.map((msg) => {
         if (msg.role === "assistant" && Array.isArray(msg.content)) {
@@ -278,16 +292,7 @@ export namespace ProviderTransform {
   export function message(msgs: ModelMessage[], model: Provider.Model, options: Record<string, unknown>) {
     msgs = unsupportedParts(msgs, model)
     msgs = normalizeMessages(msgs, model, options)
-    if (
-      (model.providerID === "anthropic" ||
-        model.providerID === "google-vertex-anthropic" ||
-        model.api.id.includes("anthropic") ||
-        model.api.id.includes("claude") ||
-        model.id.includes("anthropic") ||
-        model.id.includes("claude") ||
-        model.api.npm === "@ai-sdk/anthropic") &&
-      model.api.npm !== "@ai-sdk/gateway"
-    ) {
+    if (isClaudeModel(model) && model.api.npm !== "@ai-sdk/gateway") {
       msgs = applyCaching(msgs, model)
     }
 
diff --git a/packages/opencode/test/provider/transform.test.ts b/packages/opencode/test/provider/transform.test.ts
index 0aee396f44a3..536b641600fc 100644
--- a/packages/opencode/test/provider/transform.test.ts
+++ b/packages/opencode/test/provider/transform.test.ts
@@ -1197,6 +1197,7 @@ describe("ProviderTransform.message - anthropic empty content filtering", () =>
   test("does not filter for non-anthropic providers", () => {
     const openaiModel = {
       ...anthropicModel,
+      id: "openai/gpt-4",
       providerID: "openai",
       api: {
         id: "gpt-4",