fix(vertex): Vertex (Antropic) provider: use .rep.googleapis.com for continental multi-region endpoints (us, eu) (#28347)

Co-authored-by: Aiden Cline <aidenpcline@gmail.com>

packages/core/test/plugin/provider-google-vertex-anthropic.test.ts

@@ -2,7 +2,7 @@ import { describe, expect } from "bun:test"
 import { Effect } from "effect"
 import { Catalog } from "@opencode-ai/core/catalog"
 import { PluginV2 } from "@opencode-ai/core/plugin"
-import { GoogleVertexAnthropicPlugin } from "@opencode-ai/core/plugin/provider/google-vertex"
+import { GoogleVertexAnthropicPlugin, GoogleVertexPlugin } from "@opencode-ai/core/plugin/provider/google-vertex"
 import { ProviderV2 } from "@opencode-ai/core/provider"
 import { fakeSelectorSdk, it, model, withEnv } from "./provider-helper"
 
@@ -109,6 +109,73 @@ describe("GoogleVertexAnthropicPlugin", () => {
     ),
   )
 
+  it.effect("creates SDKs for google-vertex Anthropic models with multi-region endpoints", () =>
+    Effect.gen(function* () {
+      const plugin = yield* PluginV2.Service
+      yield* plugin.add(GoogleVertexAnthropicPlugin)
+      const result = yield* plugin.trigger(
+        "aisdk.sdk",
+        {
+          model: model("google-vertex", "claude-sonnet-4-5"),
+          package: "@ai-sdk/google-vertex/anthropic",
+          options: { name: "google-vertex", project: "project", location: "eu" },
+        },
+        {},
+      )
+      expect(result.sdk.languageModel("claude-sonnet-4-5").config.baseURL).toBe(
+        "https://aiplatform.eu.rep.googleapis.com/v1/projects/project/locations/eu/publishers/anthropic/models",
+      )
+    }),
+  )
+
+  it.effect("keeps configured baseURL for google-vertex Anthropic models", () =>
+    Effect.gen(function* () {
+      const plugin = yield* PluginV2.Service
+      yield* plugin.add(GoogleVertexAnthropicPlugin)
+      const result = yield* plugin.trigger(
+        "aisdk.sdk",
+        {
+          model: model("google-vertex", "claude-sonnet-4-5"),
+          package: "@ai-sdk/google-vertex/anthropic",
+          options: { name: "google-vertex", project: "project", location: "eu", baseURL: "https://proxy.example/v1" },
+        },
+        {},
+      )
+      expect(result.sdk.languageModel("claude-sonnet-4-5").config.baseURL).toBe("https://proxy.example/v1")
+    }),
+  )
+
+  it.effect("selects google-vertex Anthropic language models through V2 plugins", () =>
+    Effect.gen(function* () {
+      const plugin = yield* PluginV2.Service
+      yield* plugin.add(GoogleVertexPlugin)
+      yield* plugin.add(GoogleVertexAnthropicPlugin)
+      const sdkResult = yield* plugin.trigger(
+        "aisdk.sdk",
+        {
+          model: model("google-vertex", " claude-sonnet-4-5 "),
+          package: "@ai-sdk/google-vertex/anthropic",
+          options: { name: "google-vertex", project: "project", location: "us" },
+        },
+        {},
+      )
+      const languageResult = yield* plugin.trigger(
+        "aisdk.language",
+        {
+          model: model("google-vertex", " claude-sonnet-4-5 "),
+          sdk: sdkResult.sdk,
+          options: {},
+        },
+        {},
+      )
+      const language = languageResult.language as unknown as { config: { baseURL: string }; modelId: string }
+      expect(language.config.baseURL).toBe(
+        "https://aiplatform.us.rep.googleapis.com/v1/projects/project/locations/us/publishers/anthropic/models",
+      )
+      expect(language.modelId).toBe("claude-sonnet-4-5")
+    }),
+  )
+
   it.effect("trims model IDs before selecting language models", () =>
     Effect.gen(function* () {
       const plugin = yield* PluginV2.Service

packages/core/test/plugin/provider-google-vertex.test.ts

@@ -160,6 +160,32 @@ describe("GoogleVertexPlugin", () => {
     ),
   )
 
+  it.effect("keeps OpenAI-compatible Vertex endpoint templates regional for eu", () =>
+    Effect.gen(function* () {
+      const plugin = yield* PluginV2.Service
+      const catalog = yield* Catalog.Service
+      yield* plugin.add(GoogleVertexPlugin)
+      const load = yield* catalog.loader()
+      yield* load((catalog) =>
+        catalog.provider.update(ProviderV2.ID.make("google-vertex"), (provider) => {
+          provider.endpoint = {
+            type: "aisdk",
+            package: "@ai-sdk/openai-compatible",
+            url: "https://${GOOGLE_VERTEX_ENDPOINT}/v1/projects/${GOOGLE_VERTEX_PROJECT}/locations/${GOOGLE_VERTEX_LOCATION}",
+          }
+          provider.options.aisdk.provider.project = "config-project"
+          provider.options.aisdk.provider.location = "eu"
+        }),
+      )
+      const provider = yield* catalog.provider.get(ProviderV2.ID.make("google-vertex"))
+      expect(provider.endpoint).toEqual({
+        type: "aisdk",
+        package: "@ai-sdk/openai-compatible",
+        url: "https://eu-aiplatform.googleapis.com/v1/projects/config-project/locations/eu",
+      })
+    }),
+  )
+
   it.effect("defaults location to us-central1 when only project is configured", () =>
     withEnv(
       {