Anthropic SDK + Leanroute

1. Get a gateway key

From /dashboard/keys create a key labeled "anthropic-sdk". Copy the gw_live_* value.

2. Python: chat

pip install anthropic

from anthropic import Anthropic

client = Anthropic(
    api_key="gw_live_YOUR_KEY",
    base_url="https://api.leanroute.dev/anthropic",
)

msg = client.messages.create(
    model="claude-sonnet-4-6",
    max_tokens=200,
    messages=[{"role": "user", "content": "Hello in one sentence."}],
)
print(msg.content[0].text)

Note the model name is claude-sonnet-4-6 (Anthropic's native form), NOT the canonical anthropic/claude-sonnet-4-6 form we use on the OpenAI-shaped endpoint. That's deliberate — the Anthropic wire is passed through unchanged, so upstream model strings apply.

3. Python: streaming

with client.messages.stream(
    model="claude-sonnet-4-6",
    max_tokens=200,
    messages=[{"role": "user", "content": "Write a haiku about caching."}],
) as stream:
    for text in stream.text_stream:
        print(text, end="", flush=True)

4. Python: MCP passthrough

Use extra_body on the Python SDK to include mcp_servers. The SDK doesn't model that field natively yet, but it forwards unknown top-level fields transparently.

# MCP passthrough — the differentiator. mcp_servers gets forwarded
# to Anthropic and Claude will call the tool servers directly.
#
# Only per-org-allowlisted MCP URLs will pass. Configure allowlist at
# https://leanroute.dev/dashboard/mcp — unlisted URLs return 403
# mcp_server_not_allowlisted before the upstream call.
msg = client.messages.create(
    model="claude-sonnet-4-6",
    max_tokens=1024,
    messages=[{"role": "user", "content": "What are the top 3 issues on the deepwiki repo?"}],
    extra_body={
        "mcp_servers": [
            {
                "type": "url",
                "url": "https://mcp.deepwiki.com/mcp",
                "name": "deepwiki",
            }
        ],
    },
)
print(msg.content[0].text)

Response header x-gateway-mcp-allowlist reports whether the allowlist passed or blocked. Detailed guide at /docs/mcp.

5. TypeScript

npm install @anthropic-ai/sdk

import Anthropic from "@anthropic-ai/sdk";

const client = new Anthropic({
  apiKey: "gw_live_YOUR_KEY",
  baseURL: "https://api.leanroute.dev/anthropic",
});

const msg = await client.messages.create({
  model: "claude-sonnet-4-6",
  max_tokens: 200,
  messages: [{ role: "user", content: "Hello in one sentence." }],
});

console.log((msg.content[0] as { text: string }).text);

For MCP passthrough in TS use the SDK's additionalRequestOptions or pass extra fields directly — the SDK forwards unknown top-level fields.

Why route Anthropic through us at all?

Fair question — if you're only calling Claude, direct is fine. Reasons to route via Leanroute:

• Cross-provider failover: when Anthropic 529-overloads (which they do), Leanroute retries on the cheapest same-tier alternative (e.g. Sonnet 4.6 → GPT-4o / DeepSeek v4-flash) transparently.
• Per-org MCP allowlist: control which MCP servers your team can invoke centrally, without pushing config to every dev.
• Unified billing: one Stripe subscription for all your model providers instead of a separate one per vendor.
• Guardrails library: the same 7 curated rules (PII, secrets, prompt injection, moderation, data exfil, profanity, language) apply to Anthropic traffic without a separate integration.

Troubleshooting

• 401 unauthenticated: use your gw_live_* Leanroute key, NOT your Anthropic sk-ant-* key.
• 403 mcp_server_not_allowlisted: the MCP URL is not on your org's allowlist. Add it at /dashboard/mcp. The response header lists which URL failed the check.
• 404 or wrong base URL: the Anthropic endpoint lives at /anthropic (no /v1 in the base URL — the SDK appends /v1/messages itself).
• Model name rejected: use the Anthropic-native form (claude-sonnet-4-6, claude-opus-5), not the anthropic/* canonical form.