# `Puck.Compaction.Summarize`
[🔗](https://github.com/bradleygolden/puck/blob/v0.2.25/lib/puck/compaction/summarize.ex#L1)

LLM-based summarization compaction strategy.

This strategy uses an LLM to summarize older conversation history while
preserving the most recent messages verbatim. Similar to Claude Code's
`/compact` command.

Supports both ReqLLM and BAML backends transparently:
- **ReqLLM**: Pass a `:client` option with a `Puck.Client`
- **BAML**: Pass a `:client_registry` option to use Puck's built-in BAML function

## Configuration

Common options:
- `:keep_last` - Number of recent messages to preserve verbatim (default: 3)
- `:max_tokens` (required for auto-compaction) - Token threshold; `should_compact?/2`
  returns `false` unless this is set
- `:prompt` - Custom summarization prompt (optional)

ReqLLM-specific:
- `:client` (required for ReqLLM) - `Puck.Client` to use for summarization calls

BAML-specific:
- `:client_registry` (required for BAML) - Client registry map for LLM provider configuration

## How It Works

1. Splits messages: older messages to summarize vs last K messages to keep
2. Formats older messages as a conversation transcript
3. Calls the LLM with a summarization prompt
4. Returns new context: `[summary_message] ++ last_k_messages`

## Examples

ReqLLM:

    client = Puck.Client.new({Puck.Backends.ReqLLM, "anthropic:claude-sonnet-4-5"})

    {:ok, compacted} = Puck.Compaction.compact(context, {Puck.Compaction.Summarize, %{
      client: client,
      keep_last: 3
    }})

BAML (auto-detected when using BAML backend with auto_compaction):

    registry = %{
      primary: "claude",
      clients: [%{
        name: "claude",
        provider: "anthropic",
        options: %{model: "claude-sonnet-4-5", api_key: System.get_env("ANTHROPIC_API_KEY")}
      }]
    }

    {:ok, compacted} = Puck.Compaction.compact(context, {Puck.Compaction.Summarize, %{
      client_registry: registry,
      keep_last: 3
    }})

---

*Consult [api-reference.md](api-reference.md) for complete listing*