diff --git a/src/providers/proxies/claude-proxy.ts b/src/providers/proxies/claude-proxy.ts
index d8302d1..e8a249b 100644
--- a/src/providers/proxies/claude-proxy.ts
+++ b/src/providers/proxies/claude-proxy.ts
@@ -653,8 +653,19 @@ export const prepareClaudeProxyRequest = (
 
   // OAuth sessions require Claude Code identity headers.
   // https://github.com/badlogic/pi-mono/blob/5c0ec26c28c918c5301f218e8c13fcc540d8e3a4/packages/ai/src/providers/anthropic.ts#L525-L538
+  // Claude Code's Messages client uses the 2023-06-01 API version and accepts
+  // JSON even when `stream: true` requests an SSE response.
+  input.headers.delete("x-api-key");
+  input.headers.delete("cookie");
+  input.headers.delete("proxy-authorization");
+  input.headers.delete("content-encoding");
+  input.headers.delete("content-length");
+  input.headers.delete("host");
   input.headers.set("authorization", `Bearer ${input.accessToken}`);
+  input.headers.set("anthropic-version", "2023-06-01");
   input.headers.set("anthropic-beta", mergedBetas);
+  input.headers.set("accept", "application/json");
+  input.headers.set("content-type", "application/json");
   // Keep existing accounts on the minimum supported Claude Code version even
   // when their persisted metadata still contains an older user agent.
   input.headers.set("user-agent", CLAUDE_CLI_USER_AGENT);
diff --git a/tests/providers/proxy-contract.test.ts b/tests/providers/proxy-contract.test.ts
index dfadd0a..6e13636 100644
--- a/tests/providers/proxy-contract.test.ts
+++ b/tests/providers/proxy-contract.test.ts
@@ -3024,6 +3024,16 @@ describe("proxy contract: claude", () => {
   test("merges beta headers and rewrites payload tool names", () => {
     const headers = new Headers({
       "anthropic-beta": `custom-beta,${CLAUDE_REQUIRED_BETA_HEADERS[0]}`,
+      "anthropic-version": "2020-01-01",
+      accept: "text/plain",
+      "content-type": "text/plain",
+      "content-encoding": "gzip",
+      "content-length": "1234",
+      authorization: "Bearer caller-token",
+      "x-api-key": "caller-key",
+      cookie: "session=caller-cookie",
+      "proxy-authorization": "Basic caller-secret",
+      host: "caller.invalid",
     });
     const requestBody = {
       system:
@@ -3065,6 +3075,19 @@ describe("proxy contract: claude", () => {
     };
 
     expect(headers.get("authorization")).toBe("Bearer claude-token");
+    expect(headers.get("anthropic-version")).toBe("2023-06-01");
+    expect(headers.get("accept")).toBe("application/json");
+    expect(headers.get("content-type")).toBe("application/json");
+    for (const name of [
+      "x-api-key",
+      "cookie",
+      "proxy-authorization",
+      "content-encoding",
+      "content-length",
+      "host",
+    ]) {
+      expect(headers.has(name)).toBe(false);
+    }
     expect(headers.get("user-agent")).toBe(CLAUDE_CLI_USER_AGENT);
     expect(headers.get("anthropic-beta")).toBe(
       [...CLAUDE_REQUIRED_BETA_HEADERS, "custom-beta"].join(",")
@@ -3101,6 +3124,22 @@ describe("proxy contract: claude", () => {
     expect(transformed.messages[0]?.content[0]?.name).toBe("mcp_Shell");
   });
 
+  test("keeps Claude Code JSON Accept for streaming Messages requests", () => {
+    const headers = new Headers({ accept: "text/plain" });
+    prepareClaudeProxyRequest({
+      requestUrl: new URL("https://kleis.local/v1/messages"),
+      headers,
+      bodyText: '{"stream":true}',
+      bodyJson: { stream: true },
+      accessToken: "claude-token",
+      metadata: null,
+    });
+
+    expect(headers.get("accept")).toBe("application/json");
+    expect(headers.get("content-type")).toBe("application/json");
+    expect(headers.get("anthropic-version")).toBe("2023-06-01");
+  });
+
   test("rewrites repo path and directories in non-OpenCode Claude system prompts", () => {
     const requestBody = {
       system: