fix(providers): reconstruct auth headers after workflow deserialization

When a language model crosses a workflow step boundary, it is serialized
via WORKFLOW_SERIALIZE which strips function-valued config (headers, url,
fetch). On deserialization, WORKFLOW_DESERIALIZE was passing the stripped
config directly, resulting in missing auth headers and "x-api-key header
is required" errors.

Fix each provider's WORKFLOW_DESERIALIZE to reconstruct the auth headers
from environment variables when they are missing from the deserialized
config. For OpenAI models, also reconstruct the url function.

Providers fixed: Anthropic, OpenAI (chat, completion, responses),
Google, Mistral.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: gr2m

packages/anthropic/src/anthropic-messages-language-model.ts

@@ -23,6 +23,7 @@ import {
   FetchFunction,
   generateId,
   InferSchema,
+  loadApiKey,
   isCustomReasoning,
   mapReasoningToProviderBudget,
   mapReasoningToProviderEffort,
@@ -161,7 +162,22 @@ export class AnthropicMessagesLanguageModel implements LanguageModelV4 {
     modelId: AnthropicMessagesModelId;
     config: AnthropicMessagesConfig;
   }) {
-    return new AnthropicMessagesLanguageModel(options.modelId, options.config);
+    const config = { ...options.config };
+
+    // After workflow serialization, function-valued config (like headers)
+    // is stripped. Re-create auth headers from environment variables.
+    if (!config.headers) {
+      config.headers = () => ({
+        'anthropic-version': '2023-06-01',
+        'x-api-key': loadApiKey({
+          apiKey: undefined,
+          environmentVariableName: 'ANTHROPIC_API_KEY',
+          description: 'Anthropic',
+        }),
+      });
+    }
+
+    return new AnthropicMessagesLanguageModel(options.modelId, config);
   }
 
   constructor(

packages/google/src/google-generative-ai-language-model.ts

@@ -27,6 +27,7 @@ import {
   postJsonToApi,
   Resolvable,
   resolve,
+  loadApiKey,
   serializeModel,
   WORKFLOW_SERIALIZE,
   WORKFLOW_DESERIALIZE,
@@ -81,7 +82,19 @@ export class GoogleGenerativeAILanguageModel implements LanguageModelV4 {
     modelId: string;
     config: GoogleGenerativeAIConfig;
   }) {
-    return new GoogleGenerativeAILanguageModel(options.modelId, options.config);
+    const config = { ...options.config };
+
+    if (!config.headers) {
+      config.headers = () => ({
+        'x-goog-api-key': loadApiKey({
+          apiKey: undefined,
+          environmentVariableName: 'GOOGLE_GENERATIVE_AI_API_KEY',
+          description: 'Google Generative AI',
+        }),
+      });
+    }
+
+    return new GoogleGenerativeAILanguageModel(options.modelId, config);
   }
 
   constructor(

packages/mistral/src/mistral-chat-language-model.ts

@@ -16,6 +16,7 @@ import {
   generateId,
   injectJsonInstructionIntoMessages,
   isCustomReasoning,
+  loadApiKey,
   mapReasoningToProviderEffort,
   parseProviderOptions,
   ParseResult,
@@ -60,7 +61,19 @@ export class MistralChatLanguageModel implements LanguageModelV4 {
     modelId: MistralChatModelId;
     config: MistralChatConfig;
   }) {
-    return new MistralChatLanguageModel(options.modelId, options.config);
+    const config = { ...options.config };
+
+    if (!config.headers) {
+      config.headers = () => ({
+        Authorization: `Bearer ${loadApiKey({
+          apiKey: undefined,
+          environmentVariableName: 'MISTRAL_API_KEY',
+          description: 'Mistral',
+        })}`,
+      });
+    }
+
+    return new MistralChatLanguageModel(options.modelId, config);
   }
 
   constructor(modelId: MistralChatModelId, config: MistralChatConfig) {

packages/openai/src/chat/openai-chat-language-model.ts

@@ -19,9 +19,12 @@ import {
   generateId,
   isCustomReasoning,
   isParsableJson,
+  loadApiKey,
+  loadOptionalSetting,
   parseProviderOptions,
   postJsonToApi,
   serializeModel,
+  withoutTrailingSlash,
   WORKFLOW_DESERIALIZE,
   WORKFLOW_SERIALIZE,
 } from '@ai-sdk/provider-utils';
@@ -71,7 +74,31 @@ export class OpenAIChatLanguageModel implements LanguageModelV4 {
     modelId: OpenAIChatModelId;
     config: OpenAIChatConfig;
   }) {
-    return new OpenAIChatLanguageModel(options.modelId, options.config);
+    const config = { ...options.config };
+
+    // After workflow serialization, function-valued config (like headers, url)
+    // is stripped. Re-create from environment variables.
+    if (!config.headers) {
+      config.headers = () => ({
+        Authorization: `Bearer ${loadApiKey({
+          apiKey: undefined,
+          environmentVariableName: 'OPENAI_API_KEY',
+          description: 'OpenAI',
+        })}`,
+      });
+    }
+    if (!config.url) {
+      const baseURL =
+        withoutTrailingSlash(
+          loadOptionalSetting({
+            settingValue: undefined,
+            environmentVariableName: 'OPENAI_BASE_URL',
+          }),
+        ) ?? 'https://api.openai.com/v1';
+      config.url = ({ path }) => `${baseURL}${path}`;
+    }
+
+    return new OpenAIChatLanguageModel(options.modelId, config);
   }
 
   constructor(modelId: OpenAIChatModelId, config: OpenAIChatConfig) {

packages/openai/src/completion/openai-completion-language-model.ts

@@ -13,10 +13,13 @@ import {
   createEventSourceResponseHandler,
   createJsonResponseHandler,
   FetchFunction,
+  loadApiKey,
+  loadOptionalSetting,
   parseProviderOptions,
   ParseResult,
   postJsonToApi,
   serializeModel,
+  withoutTrailingSlash,
   WORKFLOW_DESERIALIZE,
   WORKFLOW_SERIALIZE,
 } from '@ai-sdk/provider-utils';
@@ -64,7 +67,29 @@ export class OpenAICompletionLanguageModel implements LanguageModelV4 {
     modelId: OpenAICompletionModelId;
     config: OpenAICompletionConfig;
   }) {
-    return new OpenAICompletionLanguageModel(options.modelId, options.config);
+    const config = { ...options.config };
+
+    if (!config.headers) {
+      config.headers = () => ({
+        Authorization: `Bearer ${loadApiKey({
+          apiKey: undefined,
+          environmentVariableName: 'OPENAI_API_KEY',
+          description: 'OpenAI',
+        })}`,
+      });
+    }
+    if (!config.url) {
+      const baseURL =
+        withoutTrailingSlash(
+          loadOptionalSetting({
+            settingValue: undefined,
+            environmentVariableName: 'OPENAI_BASE_URL',
+          }),
+        ) ?? 'https://api.openai.com/v1';
+      config.url = ({ path }) => `${baseURL}${path}`;
+    }
+
+    return new OpenAICompletionLanguageModel(options.modelId, config);
   }
 
   constructor(

packages/openai/src/responses/openai-responses-language-model.ts

@@ -22,10 +22,13 @@ import {
   generateId,
   InferSchema,
   isCustomReasoning,
+  loadApiKey,
+  loadOptionalSetting,
   parseProviderOptions,
   ParseResult,
   postJsonToApi,
   serializeModel,
+  withoutTrailingSlash,
   WORKFLOW_DESERIALIZE,
   WORKFLOW_SERIALIZE,
 } from '@ai-sdk/provider-utils';
@@ -118,7 +121,29 @@ export class OpenAIResponsesLanguageModel implements LanguageModelV4 {
     modelId: OpenAIResponsesModelId;
     config: OpenAIConfig;
   }) {
-    return new OpenAIResponsesLanguageModel(options.modelId, options.config);
+    const config = { ...options.config };
+
+    if (!config.headers) {
+      config.headers = () => ({
+        Authorization: `Bearer ${loadApiKey({
+          apiKey: undefined,
+          environmentVariableName: 'OPENAI_API_KEY',
+          description: 'OpenAI',
+        })}`,
+      });
+    }
+    if (!config.url) {
+      const baseURL =
+        withoutTrailingSlash(
+          loadOptionalSetting({
+            settingValue: undefined,
+            environmentVariableName: 'OPENAI_BASE_URL',
+          }),
+        ) ?? 'https://api.openai.com/v1';
+      config.url = ({ path }) => `${baseURL}${path}`;
+    }
+
+    return new OpenAIResponsesLanguageModel(options.modelId, config);
   }
 
   constructor(modelId: OpenAIResponsesModelId, config: OpenAIConfig) {