ServerSentEvents Req Example

Mix.install([
  {:req, "~> 0.5.17"},
  {:server_sent_events, "1.0.0"}
])

Req+Claude+SSE stream

To run this livebook, you must have a valid ANTHROPIC_API_KEY environment variable enabled for this livebook.

defmodule Claude do
  def stream_messages!(request) do
    %Req.Response{status: 200, body: response_body} =
      Req.post!("https://api.anthropic.com/v1/messages",
        json: Map.put(request, :stream, true),
        into: :self,
        headers: %{
          "x-api-key" => api_key(),
          "anthropic-version" => "2023-06-01"
        }
      )

    response_body
    |> ServerSentEvents.decode_stream()
    |> Stream.map(fn event -> JSON.decode!(event.data) end)
  end

  defp api_key do
    System.get_env("LB_ANTHROPIC_API_KEY")
  end
end

In the above module, you'll notice that we JSON.decode!/1 all events in the stream. As a slight optimization, you may choose to instead parse a subset. For example, the code below only cares about the content_block_delta event. If only that event is desired, you could filter on events with that type before JSON decoding, reducing the amount of JSON.decode calls.

stream =
  Claude.stream_messages!(%{
    model: "claude-haiku-4-5",
    max_tokens: 8192,
    system: """
    You are a poet, fluent in multiple languages and emoji usage.
    """,
    messages: [
      %{
        role: :user,
        content: "Write a poem across multiple languages and emojis!"
      }
    ]
  })

Enum.each(stream, fn event ->
  with %{"type" => "content_block_delta", "delta" => %{"text" => text}} <- event do
    IO.write(text)
  end
end)