diff --git a/src/utils/model/model.ts b/src/utils/model/model.ts
index c617f380d..ff22aff63 100644
--- a/src/utils/model/model.ts
+++ b/src/utils/model/model.ts
@@ -123,6 +123,19 @@ export function getBestModel(): ModelName {
   return getDefaultOpusModel()
 }
 
+/**
+ * Resolve the provider's primary model from its env var (e.g. OPENAI_MODEL).
+ * Returns undefined for providers that don't have a primary-model env var
+ * (Bedrock, Vertex, Foundry, firstParty).
+ */
+function getProviderPrimaryModel(): ModelName | undefined {
+  const provider = getAPIProvider()
+  if (provider === 'openai') return process.env.OPENAI_MODEL
+  if (provider === 'gemini') return process.env.GEMINI_MODEL
+  if (provider === 'grok') return process.env.GROK_MODEL
+  return undefined
+}
+
 // @[MODEL LAUNCH]: Update the default Opus model (3P providers may lag so keep defaults unchanged).
 export function getDefaultOpusModel(): ModelName {
   const provider = getAPIProvider()
@@ -138,10 +151,15 @@ export function getDefaultOpusModel(): ModelName {
   if (process.env.ANTHROPIC_DEFAULT_OPUS_MODEL) {
     return process.env.ANTHROPIC_DEFAULT_OPUS_MODEL
   }
-  // Fall back to user's configured model — custom providers may not
-  // recognize hardcoded Anthropic model IDs.
-  // Skip if the user setting is a model alias (e.g. "opus", "opus[1m]") to
-  // avoid infinite recursion: parseUserSpecifiedModel(alias) → getDefaultOpusModel().
+  // 3P providers: if user set a primary model (e.g. OPENAI_MODEL=glm-5.1),
+  // fall back to it instead of a hardcoded Anthropic model. This prevents
+  // sideQuery / background tasks from sending requests to Anthropic's API
+  // when the user configured a third-party provider.
+  const primaryModel = getProviderPrimaryModel()
+  if (primaryModel) return primaryModel
+  // Fall back to user's configured model — custom providers may not recognize
+  // hardcoded Anthropic model IDs. Skip aliases to avoid infinite recursion:
+  // parseUserSpecifiedModel(alias) → getDefaultOpusModel().
   const userSpecifiedOpus = getUserSpecifiedModelSetting()
   if (userSpecifiedOpus && !isAliasOrAliasWithSuffix(userSpecifiedOpus)) {
     return parseUserSpecifiedModel(userSpecifiedOpus)
@@ -170,9 +188,12 @@ export function getDefaultSonnetModel(): ModelName {
   if (process.env.ANTHROPIC_DEFAULT_SONNET_MODEL) {
     return process.env.ANTHROPIC_DEFAULT_SONNET_MODEL
   }
-  // Fall back to user's configured model (ANTHROPIC_MODEL / settings) —
-  // custom providers (proxies, national clouds) may not recognize the
-  // hardcoded Anthropic model IDs.
+  // 3P providers: fall back to user's primary model instead of a hardcoded
+  // Anthropic model name. Prevents background API calls from being routed to
+  // Anthropic when the user configured a third-party endpoint.
+  const primaryModel = getProviderPrimaryModel()
+  if (primaryModel) return primaryModel
+  // Fall back to user's configured model (ANTHROPIC_MODEL / settings).
   // Skip if the user setting is a model alias to avoid infinite recursion.
   const userSpecified = getUserSpecifiedModelSetting()
   if (userSpecified && !isAliasOrAliasWithSuffix(userSpecified)) {
@@ -200,9 +221,12 @@ export function getDefaultHaikuModel(): ModelName {
   if (process.env.ANTHROPIC_DEFAULT_HAIKU_MODEL) {
     return process.env.ANTHROPIC_DEFAULT_HAIKU_MODEL
   }
-  // Fall back to user's configured model — custom providers may not
-  // recognize hardcoded Anthropic model IDs.
-  // Skip if the user setting is a model alias to avoid infinite recursion.
+  // 3P providers: fall back to user's primary model instead of a hardcoded
+  // Anthropic model name.
+  const primaryModel = getProviderPrimaryModel()
+  if (primaryModel) return primaryModel
+  // Fall back to user's configured model — custom providers may not recognize
+  // hardcoded Anthropic model IDs. Skip aliases to avoid infinite recursion.
   const userSpecifiedHaiku = getUserSpecifiedModelSetting()
   if (userSpecifiedHaiku && !isAliasOrAliasWithSuffix(userSpecifiedHaiku)) {
     return parseUserSpecifiedModel(userSpecifiedHaiku)
diff --git a/src/utils/sideQuery.ts b/src/utils/sideQuery.ts
index 5557425f0..dd676a72a 100644
--- a/src/utils/sideQuery.ts
+++ b/src/utils/sideQuery.ts
@@ -35,7 +35,6 @@ import { normalizeModelStringForAPI } from './model/model.js'
 import { getAPIProvider } from './model/providers.js'
 import { getOpenAIClient } from '../services/api/openai/client.js'
 import { getGrokClient } from '../services/api/grok/client.js'
-import { anthropicMessagesToOpenAI } from '../services/api/openai/convertMessages.js'
 import { resolveOpenAIModel } from '../services/api/openai/modelMapping.js'
 import { resolveGrokModel } from '../services/api/grok/modelMapping.js'
 import {
@@ -222,10 +221,9 @@ async function sideQueryViaOpenAICompatible(
     if (openaiToolChoice) requestParams.tool_choice = openaiToolChoice
   }
 
-  const response = await client.chat.completions.create(
-    requestParams as any,
-    { signal },
-  )
+  const response = await client.chat.completions.create(requestParams as any, {
+    signal,
+  })
 
   const choice = response.choices[0]
   const message = choice?.message
@@ -303,9 +301,14 @@ async function sideQueryViaOpenAICompatible(
  * Use this instead of direct client.beta.messages.create() calls to ensure
  * proper OAuth token validation with fingerprint attribution headers.
  *
- * Third-party provider routing (OpenAI, Grok, Gemini) is handled transparently —
- * when the user configures a third-party provider, sideQuery automatically
- * routes to the correct API adapter instead of sending requests to Anthropic.
+ * This handles:
+ * - Fingerprint computation for OAuth validation
+ * - Attribution header injection
+ * - CLI system prompt prefix
+ * - Proper betas for the model
+ * - API metadata
+ * - Model string normalization (strips [1m] suffix for API)
+ * - Third-party provider routing (OpenAI, Grok, Gemini)
  *
  * @example
  * // Permission explainer
@@ -603,7 +606,8 @@ async function sideQueryViaGemini(
   const body: Record<string, unknown> = {
     contents,
     ...(systemInstruction && { systemInstruction }),
-    ...(geminiTools && (geminiTools as unknown[]).length > 0 && { tools: geminiTools }),
+    ...(geminiTools &&
+      (geminiTools as unknown[]).length > 0 && { tools: geminiTools }),
     ...(geminiToolConfig && {
       toolConfig: { functionCallingConfig: geminiToolConfig },
     }),