diff --git a/packages/mcp-core/src/internal/agents/anthropic-provider.ts b/packages/mcp-core/src/internal/agents/anthropic-provider.ts
index f2627381d..58093261c 100644
--- a/packages/mcp-core/src/internal/agents/anthropic-provider.ts
+++ b/packages/mcp-core/src/internal/agents/anthropic-provider.ts
@@ -3,7 +3,7 @@ import type { LanguageModel } from "ai";
 import { USER_AGENT } from "../../version";
 
 // Default configuration constants
-const DEFAULT_ANTHROPIC_MODEL = "claude-sonnet-4-5";
+const DEFAULT_ANTHROPIC_MODEL = "claude-sonnet-5-5";
 
 // Module-level state for baseURL (set only via explicit configuration, not env vars)
 let configuredBaseUrl: string | undefined;
@@ -21,7 +21,7 @@ export function setAnthropicBaseUrl(baseUrl: string | undefined): void {
  *
  * Configuration:
  * - ANTHROPIC_API_KEY: API key for authentication (required)
- * - ANTHROPIC_MODEL: Model to use (default: "claude-sonnet-4-5") - env var OK
+ * - ANTHROPIC_MODEL: Model to use (default: "claude-sonnet-5-5") - env var OK
  * - Base URL: Must be set via setAnthropicBaseUrl() - NOT from env vars (security risk)
  */
 export function getAnthropicModel(model?: string): LanguageModel {
diff --git a/packages/mcp-server/src/cli/usage.ts b/packages/mcp-server/src/cli/usage.ts
index c49fa4e6d..03e290ed6 100644
--- a/packages/mcp-server/src/cli/usage.ts
+++ b/packages/mcp-server/src/cli/usage.ts
@@ -26,7 +26,7 @@ Embedded agent configuration:
   --openai-base-url <url>       Override OpenAI API base URL
   --openai-model <model>        Override OpenAI model (default: gpt-5)
   --anthropic-base-url <url>    Override Anthropic API base URL
-  --anthropic-model <model>     Override Anthropic model (default: claude-sonnet-4-5)
+  --anthropic-model <model>     Override Anthropic model (default: claude-sonnet-5-5)
 
 Session constraints:
   --organization-slug <slug>  Force all calls to an organization
@@ -83,7 +83,7 @@ Embedded agent configuration:
   --openai-base-url <url>       Override OpenAI API base URL
   --openai-model <model>        Override OpenAI model (default: gpt-5)
   --anthropic-base-url <url>    Override Anthropic API base URL
-  --anthropic-model <model>     Override Anthropic model (default: claude-sonnet-4-5)
+  --anthropic-model <model>     Override Anthropic model (default: claude-sonnet-5-5)
 
 Session constraints:
   --organization-slug <slug>  Force all calls to an organization