diff --git a/src/mnemosyne/gateway.py b/src/mnemosyne/gateway.py
index 1afeb1d..e915a03 100644
--- a/src/mnemosyne/gateway.py
+++ b/src/mnemosyne/gateway.py
@@ -2587,24 +2587,43 @@ def create_app(
         }
 
         # OAuth: replace dummy x-api-key with Bearer token when available.
-        # Anthropic requires the "oauth-2025-04-20" beta header and a
-        # Claude-CLI-style user-agent for OAuth Bearer auth to be accepted.
-        # See: treplay/server.mjs proxyAnthropicContinuation()
+        # Anthropic requires specific beta headers and a Claude-CLI-style
+        # user-agent for OAuth Bearer auth to be accepted.
+        # Ref: rmk40/opencode-anthropic-auth request-headers.mjs
         oauth_token = os.environ.get("ANTHROPIC_AUTH_TOKEN")
         if oauth_token and provider == "anthropic":
             headers.pop("x-api-key", None)
             headers.pop("X-Api-Key", None)
             headers["authorization"] = f"Bearer {oauth_token}"
-            # Beta flag is REQUIRED — without it, Anthropic returns
-            # "OAuth authentication is currently not supported"
+
+            # Required beta flags — must match Claude CLI expectations.
+            _OAUTH_BETAS = [
+                "claude-code-20250219",
+                "oauth-2025-04-20",
+                "context-1m-2025-08-07",
+                "interleaved-thinking-2025-05-14",
+                "redact-thinking-2026-02-12",
+                "prompt-caching-scope-2026-01-05",
+                "advanced-tool-use-2025-11-20",
+                "effort-2025-11-24",
+            ]
+            # Add opus-specific betas if model is opus
+            model_name = req.model.lower() if req.model else ""
+            if "opus" in model_name:
+                _OAUTH_BETAS.append("context-management-2025-06-27")
+
             existing_beta = headers.get("anthropic-beta", "")
-            oauth_beta = "oauth-2025-04-20"
-            if oauth_beta not in existing_beta:
-                if existing_beta:
-                    headers["anthropic-beta"] = f"{existing_beta},{oauth_beta}"
-                else:
-                    headers["anthropic-beta"] = oauth_beta
-            headers["user-agent"] = "claude-cli/2.1.2 (external, cli)"
+            existing_set = set(b.strip() for b in existing_beta.split(",") if b.strip())
+            merged = list(dict.fromkeys(list(existing_set) + _OAUTH_BETAS))  # preserve order, dedup
+            headers["anthropic-beta"] = ",".join(merged)
+            headers["user-agent"] = "claude-cli/2.1.75 (external, cli)"
+            headers.setdefault("anthropic-dangerous-direct-browser-access", "true")
+            headers.setdefault("x-app", "cli")
+
+            # Add ?beta=true to /v1/messages URL
+            if endpoint == "messages" and "beta=true" not in upstream_path:
+                sep = "&" if "?" in upstream_path else "?"
+                upstream_path = f"{upstream_path}{sep}beta=true"
 
         if req.stream:
 
@@ -2831,13 +2850,21 @@ def create_app(
         oauth_token = os.environ.get("ANTHROPIC_AUTH_TOKEN")
         if oauth_token:
             headers["authorization"] = f"Bearer {oauth_token}"
-            existing_beta = headers.get("anthropic-beta", "")
-            oauth_beta = "oauth-2025-04-20"
-            if oauth_beta not in existing_beta:
-                headers["anthropic-beta"] = (
-                    f"{existing_beta},{oauth_beta}" if existing_beta else oauth_beta
-                )
-            headers["user-agent"] = "claude-cli/2.1.2 (external, cli)"
+            headers["anthropic-beta"] = ",".join(
+                [
+                    "claude-code-20250219",
+                    "oauth-2025-04-20",
+                    "context-1m-2025-08-07",
+                    "interleaved-thinking-2025-05-14",
+                    "redact-thinking-2026-02-12",
+                    "prompt-caching-scope-2026-01-05",
+                    "advanced-tool-use-2025-11-20",
+                    "effort-2025-11-24",
+                ]
+            )
+            headers["user-agent"] = "claude-cli/2.1.75 (external, cli)"
+            headers["anthropic-dangerous-direct-browser-access"] = "true"
+            headers["x-app"] = "cli"
         else:
             headers["x-api-key"] = api_key
         url = f"https://api.anthropic.com/v1/{path}"