Move all clients to API version 2026-10-21

The Python, TypeScript and Ruby SDK upgrades switched those clients to
2026-10-21; this brings Go and Rust along so all five send the same version.

- Go: anthropic-sdk-go v2 (new module path; no other changes needed)
- Rust: anthropic-version 2026-10-21, key sent as Authorization: Bearer
- Ruby: require anthropic >= 2.3.0
- Tests: the fake API checks the version and auth headers on every request

Author: a-akimov

mcp-client-go/go.mod

@@ -3,7 +3,7 @@ module github.com/modelcontextprotocol/quickstart-resources/mcp-client-go
 go 1.25.1
 
 require (
-	github.com/anthropics/anthropic-sdk-go v1.84.0
+	github.com/anthropics/anthropic-sdk-go/v2 v2.7.0
 	github.com/google/jsonschema-go v0.4.3
 	github.com/joho/godotenv v1.5.1
 	github.com/modelcontextprotocol/go-sdk v1.8.0

mcp-client-go/go.sum

@@ -4,8 +4,8 @@ cloud.google.com/go/auth/oauth2adapt v0.2.3 h1:MlxF+Pd3OmSudg/b1yZ5lJwoXCEaeedAg
 cloud.google.com/go/auth/oauth2adapt v0.2.3/go.mod h1:tMQXOfZzFuNuUxOypHlQEXgdfX5cuhwU+ffUuXRJE8I=
 cloud.google.com/go/compute/metadata v0.5.0 h1:Zr0eK8JbFv6+Wi4ilXAR8FJ3wyNdpxHKJNPos6LTZOY=
 cloud.google.com/go/compute/metadata v0.5.0/go.mod h1:aHnloV2TPI38yx4s9+wAZhHykWvVCfu7hQbF+9CWoiY=
-github.com/anthropics/anthropic-sdk-go v1.84.0 h1:mnAhggc5H5A98JYmhQELT+j4J89PYBFKnnSvUTNwNd8=
-github.com/anthropics/anthropic-sdk-go v1.84.0/go.mod h1:GThfYqPJoaQ/6pmibCI98Cr4y5su2FXMUHn3NrSSnIc=
+github.com/anthropics/anthropic-sdk-go/v2 v2.7.0 h1:wT62eHG7DL/ueUSJwjNQ0jRftJDSUyA2jg2wa7bNCO4=
+github.com/anthropics/anthropic-sdk-go/v2 v2.7.0/go.mod h1:LAOInMKgn6reTIrPvKXa5weyqzxsJkxSBuzhnxzukpQ=
 github.com/aws/aws-sdk-go-v2 v1.38.0 h1:UCRQ5mlqcFk9HJDIqENSLR3wiG1VTWlyUfLDEvY7RxU=
 github.com/aws/aws-sdk-go-v2 v1.38.0/go.mod h1:9Q0OoGQoboYIAJyslFyF1f5K1Ryddop8gqMhWx/n4Wg=
 github.com/aws/aws-sdk-go-v2/aws/protocol/eventstream v1.6.3 h1:tW1/Rkad38LA15X4UQtjXZXNKsCgkshC3EbmcUmghTg=

mcp-client-go/main.go

@@ -11,8 +11,8 @@ import (
 	"os/exec"
 	"strings"
 
-	"github.com/anthropics/anthropic-sdk-go"
-	"github.com/anthropics/anthropic-sdk-go/option"
+	"github.com/anthropics/anthropic-sdk-go/v2"
+	"github.com/anthropics/anthropic-sdk-go/v2/option"
 	"github.com/google/jsonschema-go/jsonschema"
 	"github.com/joho/godotenv"
 	"github.com/modelcontextprotocol/go-sdk/mcp"

mcp-client-ruby/Gemfile

@@ -2,6 +2,6 @@
 
 source "https://rubygems.org"
 
-gem "anthropic", '>= 1.72.0'
+gem "anthropic", '>= 2.3.0'
 gem "dotenv"
 gem "mcp", ">= 1.6.0"

mcp-client-ruby/Gemfile.lock

@@ -33,7 +33,7 @@ PLATFORMS
   x86_64-linux
 
 DEPENDENCIES
-  anthropic (>= 1.72.0)
+  anthropic (>= 2.3.0)
   dotenv
   mcp (>= 1.6.0)
 

mcp-client-rust/src/main.rs

@@ -22,7 +22,7 @@ const SYSTEM_PROMPT: &str =
     "You are a helpful assistant. Use the available tools when they help answer the question.";
 
 const ANTHROPIC_API_BASE: &str = "https://api.anthropic.com";
-const ANTHROPIC_VERSION: &str = "2023-06-01";
+const ANTHROPIC_VERSION: &str = "2026-10-21";
 const REQUEST_TIMEOUT: Duration = Duration::from_secs(120);
 /// Image types the Messages API accepts.
 const SUPPORTED_IMAGE_TYPES: [&str; 4] = ["image/jpeg", "image/png", "image/gif", "image/webp"];
@@ -382,7 +382,7 @@ impl MCPClient {
         let response = self
             .http
             .post(format!("{}/v1/messages", base_url.trim_end_matches('/')))
-            .header("x-api-key", api_key)
+            .bearer_auth(api_key)
             .header("anthropic-version", ANTHROPIC_VERSION)
             .json(&request)
             .send()

tests/README.md

@@ -25,7 +25,7 @@ Tool calls reach the live NWS API. When it is unreachable the tools return an er
 
 Connecting and listing tools does not exercise the chat loop, so each client is also driven through nine scripted queries with `tool-loop-test.ts`. No real API is involved: the helper starts a fake Anthropic Messages API on a loopback port and hands it to the client through `ANTHROPIC_BASE_URL`, which every quickstart SDK reads. The client talks to the mock MCP server as in the no-key test. The helper types each query only after the client shows its `Query:` prompt, as a person would.
 
-The fake API picks a script from the query text and checks every request the client sends. Every request must carry the same system prompt, and its history must be one the real API accepts: no message empty, and every `tool_use` answered by a `tool_result` in the next message.
+The fake API picks a script from the query text and checks every request the client sends. Every request must use API version `2026-10-21` and send the key as `Authorization: Bearer`, as the current SDKs do, and carry the same system prompt, and its history must be one the real API accepts: no message empty, and every `tool_use` answered by a `tool_result` in the next message.
 
 - **parallel tools** — a response with two `tool_use` blocks, then one for a tool the mock server lacks, then an answer. `tools` must be passed on every call, `max_tokens` must be 10000 (room for the model's adaptive thinking), every `tool_use` must get a `tool_result` in a single following user message with matching `tool_use_id`s, and the MCP `isError` result must be forwarded as `is_error`.
 - **ten tool turns** — exactly `MAX_TOOL_TURNS` tool calls, then an answer. The client must print the answer and no stop notice: nothing was cut short.

tests/helpers/tool-loop-test.ts

@@ -40,10 +40,11 @@
  *  - "after clear", typed after a blank line and ` clear `: the history must be
  *    empty again, and the blank line must not have been sent.
  *
- * Every request must carry the same system prompt, every query after the first
- * must carry the earlier conversation, and the history must be one the API
- * accepts: no message empty, and every tool_use answered by a tool_result in
- * the next message.
+ * Every request must use API version 2026-10-21 and send the key as a bearer
+ * token, as the current SDKs do. Every request must carry the same system
+ * prompt, every query after the first must carry the earlier conversation, and
+ * the history must be one the API accepts: no message empty, and every
+ * tool_use answered by a tool_result in the next message.
  *
  * A client that does one tool round and stops, drops `tools` on the second
  * call, sends one tool_result per message, or gets the turn cap wrong fails
@@ -112,6 +113,10 @@ const INPUT = [
   "quit",
 ];
 
+/** The API version the current SDKs send, and the Rust client sets. */
+const API_VERSION = "2026-10-21";
+const API_KEY = "test-key";
+
 /** SYSTEM_PROMPT in every client. */
 const SYSTEM_PROMPT =
   "You are a helpful assistant. Use the available tools when they help answer the question.";
@@ -131,6 +136,9 @@ type Request = {
 };
 
 const failures: string[] = [];
+/** Every anthropic-version and Authorization header the client sent. */
+const versionsSent = new Set<string>();
+const authSent = new Set<string>();
 let passed = 0;
 const calls: Record<Scenario, number> = {
   parallel: 0,
@@ -497,6 +505,8 @@ function startFakeApi(): Promise<http.Server> {
     let body = "";
     req.on("data", (chunk) => (body += chunk));
     req.on("end", () => {
+      versionsSent.add(String(req.headers["anthropic-version"]));
+      authSent.add(String(req.headers.authorization));
       let request: Request;
       try {
         request = JSON.parse(body) as Request;
@@ -540,7 +550,7 @@ function runClient(
 ): Promise<{ code: number | null; stdout: string; stderr: string }> {
   return new Promise((resolve) => {
     const child = spawn(command, args, {
-      env: { ...process.env, ANTHROPIC_BASE_URL: baseUrl, ANTHROPIC_API_KEY: "test-key" },
+      env: { ...process.env, ANTHROPIC_BASE_URL: baseUrl, ANTHROPIC_API_KEY: API_KEY },
       stdio: ["pipe", "pipe", "pipe"],
     });
     let stdout = "";
@@ -578,6 +588,10 @@ function runClient(
 /** Checks on the client's output once it has exited. */
 function checkOutput(code: number | null, stdout: string) {
   check(code === 0, `client exited 0 (got ${code})`);
+  const versions = [...versionsSent].join(", ");
+  check(versions === API_VERSION, `every request uses API version ${API_VERSION} (got ${versions})`);
+  const auth = [...authSent].join(", ");
+  check(auth === `Bearer ${API_KEY}`, `every request sends the key as a bearer token (got ${auth})`);
   check(calls.parallel === 3, `parallel: API was called 3 times (got ${calls.parallel})`);
   check(stdout.includes(FINAL_ANSWER.parallel), "parallel: client printed the final answer");